But I have trusted in thy {d} mercy; my heart shall rejoice in thy salvation.

(d) The mercy of God is the cause of our salvation.

Jamieson-Fausset-Brown Bible Commentary

5, 6. Trust is followed by rejoicing in the deliverance which God effects, and, instead of his enemy, he can lift the song of triumph.

Matthew Henry's Concise Commentary

13:1-6 The psalmist complains that God had long withdrawn. He earnestly prays for comfort. He assures himself of an answer of peace. - God sometimes hides his face, and leaves his own children in the dark concerning their interest in him: and this they lay to heart more than any outward trouble whatever. But anxious cares are heavy burdens with which believers often load themselves more than they need. The bread of sorrows is sometimes the saint's daily bread; our Master himself was a man of sorrows. It is a common temptation, when trouble lasts long, to think that it will last always. Those who have long been without joy, begin to be without hope. We should never allow ourselves to make any complaints but what drive us to our knees. Nothing is more killing to a soul than the want of God's favour; nothing more reviving than the return of it. The sudden, delightful changes in the book of Psalms, are often very remarkable. We pass from depth of despondency to the height of religious confidence and joy. It is thus, ver. 5. All is gloomy dejection in ver. 4; but here the mind of the despondent worshipper rises above all its distressing fears, and throws itself, without reserve, on the mercy and care of its Divine Redeemer. See the power of faith, and how good it is to draw near to God. If we bring our cares and griefs to the throne of grace, and leave them there, we may go away like Hannah, and our countenances will be no more said, 1Sa 1:18. God's mercy is the support of the psalmist's faith. Finding I have that to trust to, I am comforted, though I have no merit of my own. His faith in God's mercy filled his heart with joy in his salvation; for joy and peace come by believing. He has dealt bountifully with me. By faith he was as confident of salvation, as if it had been completed already. In this way believers pour out their prayers, renouncing all hopes but in the mercy of God through the Saviour's blood: and sometimes suddenly, at others gradually, they will find their burdens removed, and their comforts restored; they then allow that their fears and complaints were unnecessary, and acknowledge that the Lord hath dealt bountifully with them.