Albert Barnes 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 shall count – That is, God himself will honor those who are so born. In the previous verse, the effect of such a birth was described as securing honor from human beings. Here a higher honor is referred to – that which will be derived from God himself.

When he writeth up the people ... – The word rendered “people” here is in the plural number. At the time of making an enrollment of the people, or taking an account or a census of the nations, he would mark, or cause to be marked, with special honor the man who was born in Zion. From among them his own people would be taken, and those so born would have an honor which no one else would receive from him. He would not mark with any special approval those who had been born in Egypt, in Babylon, or in Tyre, but he would mark with special interest those who had been born in Zion.

The practical truth suggested here is that God will, for the most part, take his people from among those who have been born in the church. As a matter of fact, while it is true that others are converted and added to the church, the great mass of church members consist of those who have been born of Christian parents, who have been dedicated to God early in life, and who have been trained for his service. See the notes at (Isaiah 44:3–5).