…to take ‘God’s righteousness’ as referring to the righteous status given by God agrees better with the structure of the argument of the epistle, in which 1.18-4.25 expounds the words ‘he who is righteous by faith’ and 5.1-8.39 the promise that the man who is righteous by faith ‘shall live’. If 2.13; 3.20;, 28; 4.2, 13; 5.1, 9, 19, are examined carefully, it will be seen that it is on the status resulting from God’s action and on the men on whom the status is conferred rather than on the actual actions of God that attention is focused.
The sense of the whole sentence, as we understand it, may be set out as follows: For in it (that is, in the gospel as it is being preached) a righteous status before God which is God’s gift is being revealed (and so offered to men), a righteous status which is altogether by faith. …by revealing and making available precisely this gift of a status of righteousness before Himself God is indeed acting mightily to save.
As used by [Paul], ‘faith’ has the same sense as it has in the earlier part of v. 17 and ‘shall live’ refers, not to political survival, but to the life of God, which alone is true life, the life which the believer begins to enjoy here and now, and will enjoy in its fullness hereafter.