In the book of Galatians, Paul famously establishes an either/or binary of salvation "by works," ἐκ νόμου, and "by faith," ἐκ πίστεως. In substantiating this mutually exclusive dichotomy (ὁ δὲ νόμος οὐκ ἔστιν ἐκ πίστεως, 3:12), he quotes from Habakkuk 2:4 and Leviticus 18:5 respectively:
ὁ δίκαιος ἐκ πίστεως ζήσεται
ὁ ποιήσας αὐτὰ ζήσεται ἐν αὐτοῖς
The implied contrast is between the doing of the law (ὁ ποιήσας αὐτὰ…, Lev 18:5; cf. Eze 20:11, 13, 21; 18:5-9; Neh 9:29; etc.; and Gal 3:10b, ἐμμένει πᾶσιν τοῖς γεγραμμένοις ἐν τῷ βιβλίῳ τοῦ νόμου τοῦ ποιῆσαι αὐτά, citing Dt 27:26; cf. Ro 10:5, where Lev 18:5 is referenced as τὴν δικαιοσύνην τὴν ἐκ νόμου) and the simple act of “hearing with faith,” as he argues explicitly in Gal 3:1-5 (cf. Ro.2:13). According to the apostle, salvation is either ἐξ ἔργων νόμου ἢ ἐξ ἀκοῆς πίστεως (3:5b), and from our experience we know it is ἐξ ἀκοῆς πίστεως.
But Paul reasons from the scriptures as well. Was this not how our father Abraham was justified before God (Gal.3:6-7), by faith, by believing what he heard from God before he was circumcised (as he argues in Romans 4:1ff., and before the binding of Isaac in Genesis 22, cf. Jas.2:21-23)? This is an important point in the context of first century Judaism. Abraham’s justification was traditionally seen as based on his obedience. In 1Macc.2:52, for instance, we read: “Abraham was found faithful (εὑρέθη πιστός) in temptation, and it was reckoned to him as righteousness.” In fact, in some witnesses of ancient Judaism, there were 10 tests for Abraham culminating in the so-called Akedah (binding of Isaac). In proving faithful during these tests, Abraham’s obedience was understood as meritorious, compensating for future Israel’s (constant) breaking of the 10 commandments of Moses. Because the law was understood as the eternal instrument through which God blessed His people, even Abraham’s justification was interpreted as the result of his obedience to the law (in principle, as it was not yet delivered to Israel as it would be at the theophany in Sinai). In so doing, the distinction between believing God’s promises and doing His commandments was typically lost, conflated under a single rubric: faithfulness (πιστός). As Ridderbos notes, "How much Paul's appeal to Hab.2:4; Gen.15:6, et al., proceeds from an entirely different concept of faith from that of the Jewish religion of law, in which "faith" is simply subsumed under "works," has anew become clearly apparent from the interpretation of Hab.2 in the pesher on Hab. (IQpHab 7.18ff.) found at Qumran, where the words "but the just shall live by his faith" are applied to all the doers of the Torah in the house of Judah, whom God will save "out of the house of judgment" on the ground of their work and of their faith in (or faithfulness to) the teacher of righteousness."
However, Paul is at pains here to show that it was through faith, apart from any works (i.e., law observance), that the patriarch was blessed, and so we too are blessed through faith alone according to the promise (3:8-9). As John Chrysostom writes, “they [the Judaizers] said that he who adhered to Faith alone was cursed, but he shows that he who adhered to Faith alone is blessed.” In fact, Paul argues (3:10), rather than blessing, the law of Moses brings curse (Dt 27:26), since under the law we are exposed as guilty before God, as the Writings and Prophets also bear witness: ὅτι δὲ ἐν νόμῳ οὐδεὶς δικαιοῦται παρὰ τῷ θεῷ δῆλον (3:11a; cf. Rom.3:9-20). Accordingly, Paul earlier writes: ἐξ ἔργων νόμου οὐ δικαιωθήσεται πᾶσα σάρξ, 2:16b (cf. ἐξ ἔργων νόμου οὐ δικαιωθήσεται πᾶσα σὰρξ ἐνώπιον αὐτοῦ, Rom.3:19). Here he is echoing Psalm 143:2: ὅτι οὐ δικαιωθήσεται ἐνώπιόν σου πᾶς ζῶν.
This conclusion then is the unspoken premise in Paul’s argument regarding the curse of the law in Gal.3:10. All who are under the law transgress the law (cf. 3:18), and so, rather than being justified by it, are “imprisoned under sin” (3:22; cf. Ro 3:19). However, Paul continues, it is clear elsewhere from Scripture - namely, Habakkuk 2:4 - that the blessing / righteousness / life promised to God’s people is not and never was given through or “by the law”:
Now it is evident that no one is justified before God by the law, for “The righteous shall live by faith.” But the law is not of faith, rather “The one who does them shall live by them.”
It is noteworthy that, having quoted from the prophet that "the righteous shall live by faith,” he then stresses that the (way of the) law is not (the way) of faith. Paul is clarifying that the path to life spoken of in Habakkuk is fundamentally different than the conditional life offered in the law (and repeated throughout the Prophets). To substantiate this claim, Paul cites the law - namely, Lev 18:5 - in a manner that deliberately mimics the grammatical structure of Hab 2:4 in order to highlight the dramatic contrast between “the righteous by faith” and “the doer of the law,” (3:12b). This appears to be a momentous step in the argument, because, as Longnecker writes, “The rabbis seem to have coupled Hab 2:4 with Gen 15:6 as important testimonia having to do with the nation’s inerhitance of Abraham's meritoroius faith (cf. Exod.Rab. 23.5), viewing Hab 2:4 in particular as the summation of the whole Mosaic law in one principle.” Cf. 1QpHab 7.14-8.3, referenced above. Paul likewise connects these two texts, but with a radically different emphasis: faith (as hearing and believing) vs. faithfulness (as law observance).
We should say here that Paul would not have decoupled faith from faithfulness absolutely. The dichotomy he’s stressing isn’t faith as belief and faithfulness as obedience per se, but rather faith and law observance as the grounds of justification, and so of securing Abraham’s promise. As Moises Silva writes, “for Habakkuk there was no dichotomy between faith and faithfulness…That the apostle Paul did not view justifying faith as excluding obedience to God’s commandments is suggested in Galatians itself (see esp. 5:13-26…), but the organic link between these two concepts is extensively developed in Romans,” in which the apostle also cites Hab 2:4 as foundational to his gospel (Rom 1:17). Rather, "we must not suppose that doing the commandments as the way of life has ceased to have any validity or application," John Murray contends, but "bear in mind that righteousness and life are never separable... In the realm of grace, therefore, obedience is the way of life... It is this principle that appears in Lev.18:5," (emphasis added). Cf. Jas 1:22-25 (οὐκ ἀκροατὴς ἐπιλησμονῆς γενόμενος ἀλλὰ ποιητὴς ἔργου, οὗτος μακάριος ἐν τῇ ποιήσει αὐτοῦ ἔστα). Having said that, Paul is very clearly citing this verse in antithesis with Hab 2:5 to distinguish faith as “hearing and believing” from the “doing" of the law as the means of receiving Abraham's blessing - a distinction, as noted above, that appears to have been entirely obscured or even foreign in first century Judaism.
But should אֱמוּנָה be read as emphasizing one’s “faith,” as the apostle seems to presuppose here and in Romans 1:17 (and, I would argue, the author of Hebrews does in Heb 10:38, especially in light of his definition of πιστός in 11:1), or as an objective faithfulness, as it most often means in similar uses w/in the MT (e.g., 2Chr 19:9; Ps 37:3, Pro 12:22, Isa 11:5)? The distinction is especially important in this context, since the objective sense of “faithfulness” seems far too ambiguous to be of much use in Paul’s debate with the Judaizers (or his unbelieving Jewish opponents) regarding the role of law observance in justification. It is also noteworthy that Hab 2:4 (LXX) is the only occurance of the theologically loaded construction ἐκ πίστεως in the Septuagint. So the question is whether Paul violates the typical meaning of אֱמוּנָה here by “forcing” it into an anachronoistic, Christian category - “by faith." The related question of whether “life” here refers to survival of the coming Chaldean invasion or to an eschatological life that transcends the events of the 6th/7th century will not be here addressed except to say that the eschatological notion undoubtedly lurks in all the covenant promises of national life rehearsed in both Moses and the Prophets (a point that seems to not have escaped the rabbis: “And you shall keep My statutes, and the order of My judgments, which if a man do he shall live in them, in the life of eternity, and his portion shall be with the just.” and live by them: in the World-To-Come. For if you say [that the verse refers to living] in this world, does he not eventually die? [Torath Kohanim 18:134]). At the very least, we may say that Paul (and other rabbis) read Hab 2:4 as indicating an enduring, general principle: the rigtheous will live by their faith/fulness.
Paul’s citation (ὁ δίκαιος ἐκ πίστεώς ζήσεται) is fairly close to the LXX(B)’s translation:
ἐὰν ὑποστείληται, οὐκ εὐδοκεῖ ἡ ψυχή μου ἐν αὐτῷ, ὁ δὲ δίκαιος ἐκ πίστεώς μου ζήσεται
Now the differences of this rendering from that of the MT have often been noted. Paul’s dropping of the pronominal suffix (whether yod, as the MT has it, or waw, as the LXX reflects) does not substantially change the sense of the text (if it does, it is hard to see how Paul isn’t manipulating the text rather than faithfully(!) reasoning from it, and it is even less clear how such a distortion would be convincing to his critics). But it is also striking that the LXX translates the obscure Hebrew verb עֻפְּלָ֔ה as “draws back” (ὑποστείληται). In the only other occurance of this root (עפּל) in the MT, Nu 14:44a, it is translated with a near antonym, διαβιάζομαι: an intensified form of βιάζομαι (cf. Lk 16:16; Mt 11:12). It is perhaps noteworthy that the fundamental issue Moses draws out in Numbers 14 regarding this disasterous episode in Israel’s history is the people’s unbelief (see Nu 14:11 [לֹא־יַאֲמִ֣ינוּ], and Moses' subsequent commenatry on the same event in Dt 1:32 [אֵֽינְכֶם֙ מַאֲמִינִ֔ם]). The entire re-narration of these events in Dt 1-3 appears to be a chastising of Israel’s unbelief regarding the promises of God in the conquest of Canaan (cf. Dt 9:23). Even Moses and Aaron were forbidden entrance into the land because they apparently acted in unbelief (לֹא־הֶאֱמַנְתֶּ֣ם בִּ֔י, Nu 20:12). Of course, the author of Hebrews understands the entire debacle in the wilderness to have been due to the unbelief of the first generation (Heb 3:19-4:2). Interestingly, the consturction in Nu 14:11 (לֹא־יַאֲמִ֣ינוּ) is the same form as found in Habakkuk 1:5 (לֹ֥א תַאֲמִ֖ינוּ).
But going back to the strange verb in Hab.2:4a, the Septuagint rightly renders the sense in Num.14:44, especially in light of its parallel in Dt 1:43 (וַתָּזִ֖דוּ; cf. Neh 9:29). Indeed, the picture of a “presumptious” action, rendered in Num.14:44 LXX as a violent penetration or thrust forward, is accurately characterized by a “puffing up” or arrogant condition. So how do we explain the LXX’s rendering in Habakkuk 2:4, "drawing back”? Most scholars have explained it by supposing that the Greek translators transposed two characters of the verb עפּל to עלף, meaning “to faint” (though, as Carl Armerding well argues, עפּל is the preferred reading). It is argued that this transposition was influenced by the preceding verse, 2:3, where the one who hears the message is told to “wait” patiently for it. If so, the ancient translators apparently understood 2:4 as referencing not the Chaldeans per se (as the context and language of the MT might initially suggest), but the one who hears and does not trust or believe, and so “draws back”. This sense certainly coheres with the author of Hebrews' use of Hab 2:3-4 in Heb 10:38 (though he reverses the order of the verses). But what if we don't speculate that עפּל was transposed, but suppose rather it was rendered ὑποστείληται as the result of a dynamic translation based on both the immediate literary context (2:3) and intertextual dependence upon the Pentateuch’s account of the first generation's failure to enter the land? After all, διαβιάζομαι is itself hardly a straightfoward rendering of the root עפּל in Num 14:44. It is more an interpreted rendering. But in both cases, the word defines the faithless response to God's Word, though in vastly different forms: here a fearful retreat rather than a foolhardy advance forward. But whatever the case, the LXX's rendering of “draw back" in 2:4 (and perhaps the reversed order cited in Heb 10:38) was undoubtedly shaped by an understanding of the command “to wait” in 2:3 as implying an enduring faith or belief in God’s Word (Hab 2:2-3; cf. Ps 33:20-21; 27:13-14).
Furthermore, the posited intertextuality can be demonstrated by the multiple, striking parallels found between Habakkuk and the Pentateuch (e.g., Ex 15; Dt 32-33 and Hab 3; Nu 14:11; Dt 1:32 and Hab 1:5; Nu 14:20 and Hab 2:14 [Isa 11:9]; etc.). As scholars have often pointed out, Habakkuk seems to paint the picture of Israel’s coming salvation in the Mosaic colors of her foundational redemption from Egypt, drawing both his imagery and language directly from Exodus, Numbers and Deuteronomy. And since, as already noted, the assessments recorded in Nu.14:11, 20:12 and Dt 1:32 indicate - together with the later reflections of inspired authors (e.g., Ps 78:22, 32; 106:24; 2Ki.17:14) - that the primary threat to Israel’s receiving the promised blessing of Abraham was their lack of faith in God’s promise and power, then it is very conceivable that Habakkuk is comprehending this when he writes: וְצַדִּ֖יק בֶּאֱמוּנָתוֹ֥ יִחְיֶֽה.
Even if 2:4a references the Chaldeans, and is more accurately rendered “swollen” or ‘prideful” contrary to the LXX and ala Nu 14:44 (LXX), it is also possible that the intertextual dependence of Habakkuk 2 on Nu 14 (and Dt 1-3) is intended to convey in 2:4a a response that lacks faith, such that the contrasted parallelism of 2:4b is designed to describe the blessed response of faith.
If reading these connections between Habakkuk and the particular accounts of Israel’s failure to receive the promises, as recorded in the Pentateuch broadly, and the connections between Hab 2 and Nu 14 more specifically, is warranted, then it seems the phrase ἐκ πίστεώς in the LXX is accurately rendered, “by his faith”/“by faith in me" (of course with the implication that this belief/trust will persevere, that is, wait patiently, as well as render ongoing obedience to God’s word, through which this faith subsists), rather than merely “by his faithfulness." If this is the case, Paul had good reason to cite ἐκ πίστεώς in Hab.2:4 as signifying “by faith” (certainly a persevering and obedient faith), rather than the more ambiguous “by faithfulness,” rendered moot by the prevailing Judaistic conception of law observance.
Moreover, as has been argued elsewhere, this “by faith” rendering makes good sense within the MT of Habakkuk. Doesn’t the prophet himself embody the righteous man who by faith waits for the Word of the Lord to come to fruition? As Thomas Schreiner writes,
Habakkuk predicts a day of judgment when the Chaldeans will punish sinful Judah because the nation failed to keep God’s Torah (1:4-11). Such a judgment is a test of faith for the remnant (cf. 1:5). Will they still believe God’s promises, which include a future judgment of Babylon (ch.2) and a future renewal of the work of the exodus for Israel (ch.3)? The many allusions to the exodus in Hab 3 indicate the promise of a new exodus, a new deliverance for the people of God. Hence, Habakkuk functions as a paradigm for the people of God. He will continue to trust the Lord even if the fig tree does not blossom and vines are lacking fruit (Hab 3:17-18). He will continue to trust in and rejoice in God’s promise of future salvation. … This is not to deny that faithfulness flows from faith, for the former always proceeds from the latter. Faith is the foundation and faithfulness is the superstructure. It follows that Paul is a brilliant interpreter of Habakkuk and does not distort its message but capsulizes it.