God be merciful unto us, and bless us - There is, perhaps (as Prof. Alexander suggests), an allusion, in the language used here, to the sacerdotal benediction in Numbers 6:24-26 : “The Lord bless thee, and keep thee; the Lord make his face shine upon thee, and be gracious unto thee: the Lord lift up his countenance upon thee, and give thee peace.” The prayer is that God would bestow upon his people the blessing implied in the form of benediction which he had directed the ministers of his religion to use. The first cry is, of course, for mercy or favor. The beginning of all blessings to mankind is the favor or mercy of God. There is no higher blessing than his favor; there is none that comes from him which should not be regarded as mercy.
And cause his face to shine upon us - Margin, With us. That is, among us. It is an invocation of his presence and favor. On the phrase “cause his face to shine,” see the notes at Psalms 4:6.