Galatians 2:16

οὐ δικαιοῦται … Two methods of seeking justification in the sight of God are here distinguished. The former took account of nothing but stedfast obedience to the law of God. Before his conversion Paul knew no other: he had been taught by his legal training to base his standard of right and wrong entirely on the revealed law, to find in it the sole guide of conscience, and to measure righteousness by conformity to its commandments alone.

But his view of God's judgment had been profoundly modified by his conversion. He had learnt on the one hand from the teaching of Christ how impossible it was for man to attain to perfect righteousness, seeing that God claims not only obedience to the letter of the law, but an allegiance of the heart too thorough to be attainable by human infirmity. But on the other hand he knew now that God is a loving Father in Christ, ever seeking out His erring children that He may win them back, ever ready to temper strict justice with infinite mercy, and waiting only for the first response of imperfect faith and imperfect repentance, so they be at all sincere, to blot out a guilty past, and pronounce a favourable judgment on the sinner. He perceived that there is room in the judgment of God for another element beside strict justice, viz., the mercy of the judge, and that a prisoner, however clear may be his guilt on the evidence of his life, may nevertheless be assured of pardon and acceptance by throwing himself in humble trust on that mercy. In the Epistles of Paul accordingly justification acquired a new meaning, becoming equivalent to acceptance before God, and the term righteousness was applied to the merciful acquittal of the guilty but penitent offender.

The clause ἐξ ἔργων νόμου defines an acquittal on the merits of the case alone, based on a life of holy obedience, while διὰ πίστεως Ἰ. Χρ. points to faith in Christ as the appointed channel of God's mercy. ἐπιστεύσαμεν. Here, as in Romans 13:11, this verb denotes the act of embracing the faith. Jewish Christians had by their conversion declared the hopelessness of their position under the Law without Christ. Faith in him was (they saw) the only means of obtaining justification. διότι … This clause corroborates the verdict of conscience and experience by the authority of Scripture, for it adopts the language of Psalms 142 (143) 2, οὐ δικαιωθήσεται ἐνώπιόν σου πᾶς ζῶν, with only some verbal alterations suggested by the context of the Epistle. As two kinds of justification have been mentioned, the clause ἐξ ἔργων νόμου is required here to make it clear that the justification to which the Psalm refers was legal, the words ἐνώπιόν σου are dropped as needless in this context, and πᾶσα σάρξ is substituted for πᾶς ζῶν in order to show that the Psalm referred to earthly life. The passage is quoted with corresponding verbal changes in Romans 3:20.