John Calvin Commentary Psalms 87:6

"Jehovah will count, when he writeth up the peoples, This one was born there. Selah" — Psalms 87:6 (ASV)

The Lord will recount, when he writeth the peoples. The meaning is that Zion will acquire such renown that it will stir all people with the greatest earnestness to desire to be included in the number and rank of her citizens. This describes a highly honorable condition. The language implies that when God takes a census of the people on whom He will be graciously pleased to confer the highest honor, He will write them as belonging to Zion, rather than to Babylon or any other cities. For to be one of the common people among Zion's citizens will be a greater distinction than to hold the highest rank anywhere else.

At the same time, we are taught that the source of the sudden elevation of these foreigners to such great honor is the favor of God. Those who are the bondslaves of Satan and of sin will certainly never be able to obtain, through any efforts of their own, the right of citizenship in the heavenly Jerusalem.

It is the Lord’s distinctive work to divide people into their respective ranks, distinguishing one from another as seems good to Him, for all people are by nature on the same level. This passage is to be understood as referring to effectual calling. God, it is true, wrote the names of His children in the Book of Life before the creation of the world; but He enrolls them in the register of His saints only when, having regenerated them by the Spirit of adoption, He impresses His own mark upon them.