But I have trusted in thy mercy - Thou wilt not suffer me to fall; or if I have fallen, wilt thou not, for his sake who died for sinners, once more lift up the light of thy countenance upon me? Wilt thou not cover my sin?
My heart shall rejoice in thy salvation - There is no true joy but of the heart; and the heart cannot rejoice till all guilt is taken away from the conscience.
But I have trusted in thy mercy - In thy favor; thy friendship; thy promises. His original confidence had been in God only, and not in himself. That confidence he still maintained; and now, as the result of that, he begins to exult in the confidence that he would be safe. The idea is, “I have trusted in the mercy of God; I still trust, and I will trust forever.”
My heart shall rejoice in thy salvation - The word “salvation” here does not refer to salvation in the future world, but to deliverance from his present troubles, or to God‘s interposition in putting him into a condition of safety. The idea is, that he had entire confidence that God would interpose, and that there would yet be cause to rejoice in that salvation as actually accomplished. He now calls on his heart to rejoice in the assurance that it would be his. So with us. There will not only be rejoicing in salvation when actually accomplished, but there may, and should be, in the firm conviction that it will be ours.