Let thy mercy be on us, O Jehovah! At length the psalm concludes with a prayer, which the sacred writer offers in the name of all the godly, that God would make them feel from the effect that they have not relied on the divine goodness in vain. In the meantime, the Spirit, by dictating to us this rule of prayer by the mouth of the prophet, teaches us, that the gate of divine grace is opened for us when salvation is neither sought nor hoped for from any other quarter. This passage gives us another very sweet consolation, namely, that if our hope faint not in the midst of our course, we have no reason to fear that God will fail to continue his mercy towards us, without intermission, to the end of it.

Let thy mercy, O Lord, be upon us - Let us find or obtain thy mercy or thy favor.
According as we hope in thee - It may be remarked in regard to this:
(a) it is but "reasonable" that we should look for the favor of God only as we trust in him, for we could not with propriety expect his favor beyond the measure of our confidence in him.
(b) This may be regarded as the most that we are entitled to hope from God. We have no reason to suppose that he will go beyond our wishes and prayers, or that he will confer favors on us which we neither expect nor desire.
(c) One of the reasons why the people of God are no more blessed, or why they receive no more favors from him, may be found in what is here suggested. As they expect little, they obtain little; as they have no intense, burning, lofty desire for the favor of God, either for themselves personally, or for their families, or for the world, so they obtain but slight tokens of that favor.
(d) The true principle, therefore, upon which God is willing to bestow His favors, and which will be the rule that He will observe, is, that if people desire much, they will obtain much; that if they have big expectations, they will not be disappointed; and that God is willing to bestow His mercies upon His people and upon the world to the utmost of their desires and hopes. Compare Psalm 81:10, "Open thy mouth wide, and I will fill it." Psalm 37:4, "delight thyself in the Lord, and he shall give thee the desires of thy heart." How intense and fervent, then, should be the prayers and the petitions of the people of God! How earnest the supplications of sinners that God would have mercy on them!

Let thy mercy, O Lord, be upon us - We cannot abide in this state unless upheld by thee; and, as we disclaim all merit, we seek for a continuance of thy mercy, and this we cannot expect but in a continual dependence on thee. "Let thy mercy, O Lord be upon us, according as we hope in thee."

Let thy mercy, O Lord, be upon us,.... That is, an application of it in its effects: it is a prayer for a communication of grace and mercy to help in a time of need; and for a discovery of pardoning grace and mercy; and it is a prayer of faith; for the mercy of the Lord is upon his people in great plenty, and it continues; and they have reason to believe it ever will, Psalm 103:17;
according as we hope in thee; not according to any merits of theirs, but according to the measure of grace, of the grace of hope which God had bestowed on them, and encouraged them to exercise on him, in expectation of finding grace and mercy with him.