John Calvin Commentary Psalms 51:18

"Do good in thy good pleasure unto Zion: Build thou the walls of Jerusalem." — Psalms 51:18 (ASV)

Do good to Zion in thy good pleasure: build thou the walls of Jerusalem, from prayer on his own behalf, he now proceeds to offer supplications for the collective Church of God, a duty which he may have felt to be the more incumbent on him because by his fall he had done all he could to ruin it. Raised to the throne, and originally anointed to be king for the very purpose of fostering the Church of God, he had by his disgraceful conduct nearly accomplished its destruction.

Although chargeable with this guilt, he now prays that God would restore it by His free mercy. He makes no mention of the righteousness of others, but rests his plea entirely upon the good pleasure of God, intimating that the Church, whenever it has been brought low, owes its restoration solely to Divine grace.

Jerusalem was already built, but David prays that God would build it further, for he knew that it fell far short of being complete as long as it lacked the temple, where He had promised to establish the Ark of His Covenant, and also the royal palace. We learn from the passage that it is God’s own work to build the Church.

His foundation, says the Psalmist elsewhere, is in the holy mountains, (Psalms 87:1). We are not to imagine that David refers simply to the Church as a material structure, but must consider him as having his eye fixed upon the spiritual temple, which cannot be raised by human skill or industry.

It is true, indeed, that men will not make progress even in the building of material walls unless their labor is blessed from above; but the Church is in a peculiar sense the building of God, who has founded it on the earth by His mighty power, and who will exalt it higher than the heavens.

In this prayer David does not contemplate the welfare of the Church merely for a short period, but prays that God would preserve and advance it until the coming of Christ. And here, is it not justly surprising to find someone who, in the preceding part of the psalm, had used the language of distress and almost despair, now inspired with the confidence necessary to commend the whole Church to God's care?

How does it happen, we might ask, that someone who so narrowly escaped destruction himself should now appear as a guide to lead others to salvation? In this we have a striking proof that, provided we obtain reconciliation with God, we may not only expect to be inspired with confidence in praying for our own salvation, but may also hope to be accepted as intercessors on behalf of others, and even be advanced to the still higher honor of commending the glory of the Redeemer’s kingdom into the hands of God.