16 But now in days that are as yet evil, let us speak as follows. “Look upon Your servants, and upon Your works”. For Your servants themselves are Your works, not only inasmuch as they are men, but as Your servants, that is, obedient to Your commands. For we are His workmanship, created not merely in Adam, but in Christ Jesus, unto good works, which God has before ordained that we should walk in them: “for it is God which works in us both to will and to do of His good pleasure.” “And direct their sons:” that they may be right in heart, for to such God is bountiful; for “God is bountiful to Israel, to those that are right in heart.”...
17. “And let the brightness of the Lord our God be upon us”; whence the words, “O Lord, the light of Your countenance is marked upon us.” And, “Make Thou straight the works of our hands upon us:” that we may do them not for hope of earthly reward: for then they are not straight, but crooked. In many copies the Psalm goes thus far, but in some there is found an additional verse at the end, as follows, “And make straight the work of our hands.” To these words the learned have prefixed a star, called an asterisk, to show that they are found in the Hebrew, or in some other Greek translations, but not in the Septuagint. The meaning of this verse, if we are to expound it, appears to me this, that all our good works are one work of love: for love is the fulfilling of the Law. For as in the former verse he had said, “And the works of our hands make Thou straight upon us,” here he says “work,” not works, as if anxious to show, in the last verse, that all our works are one, that is, are directed with a view to one work. For then are works righteous, when they are directed to this one end: “for the end of the commandment is charity out of a pure heart, and of a good conscience, and of faith unfeigned.” There is therefore one work, in which are all, “faith which works by love:” whence our Lord's words in the Gospel, “This is the work of God, that you believe in Him whom He has sent.” Since, therefore, in this Psalm, both old and new life, life both mortal and everlasting, years that are counted for nought, and years that have the fullness of loving-kindness and of true joy, that is, the penalty of the first and the reign of the Second Man, are marked so very clearly; I imagine, that the name of Moses, the man of God, became the title of the Psalm, that pious and right-minded readers of the Scriptures might gain an intimation that the Mosaic laws, in which God appears to promise only, or nearly only, earthly rewards for good works, without doubt contains under a veil some such hopes as this Psalm displays. But when any one has passed over to Christ, the veil will be taken away: and his eyes will be unveiled, that he may consider the wonderful things in the law of God, by the gift of Him, to whom we pray, Open Thou my eyes, and I shall see the wondrous things of Your law.
Source: The Enarrations, or Expositions, on the Psalms (New Advent)