And it shall be our {l} righteousness, if we observe to do all these commandments before the LORD our God, as he hath commanded us.

(l) Because no one can fully obey the law, we must turn to Christ to be justified by faith.

Wesley's Notes

6:25 It shall be our righteousness - Heb. Righteousness shall be to us. We shall be owned and pronounced by God to be righteous and holy persons, if we sincerely obey him, otherwise we shall be declared to be unrighteous and ungodly. Or, mercy shall be to us, or with us. For as the Hebrew word rendered righteousness is very often put for mercy, (as Psa 24:5 36:10 51:14 Pro 10:2 11:4 Dan 9:16) so this sense seems best to agree both with the scripture use of this phrase, (in which righteousness, seldom or never, but grace or mercy frequently, is said to be to us or with us) and with the foregoing verse and argument God, saith he, Deu 5:24, commanded these things for our good, that he might preserve us alive, as it is this day. And, saith he in this verse , this is not all; for as he hath done us good, so he will go on to do us more and more good, and God's mercy shall be to us, or with us, in the remainder of our lives, and for ever, if we observe these commandments.

Matthew Henry's Concise Commentary

6:17-25 Moses gives charge to keep God's commandments. Negligence will ruin us; but we cannot be saved without diligence. It is our interest, as well as our duty, to be religious. It will be our life. Godliness has the promise of the continuance and comfort of the life that now is, as far as it is for God's glory. It will be our righteousness. It is only through the Mediator we can be righteous before God. The knowledge of the spirituality and excellency of the holy law of God, is suited to show sinful man his need of a Saviour, and to prepare his heart to welcome a free salvation. The gospel honours the law, not only in the perfect obedience of the Son of God, the Lord Jesus Christ; but in that it is a plan for bringing back apostate rebels and enemies, by repentance, faith, forgiveness, and renewing grace, to love God above all things, even in this world; and in the world above, to love him perfectly, even as angels love him.