Psalms 87:6

The Lord shall count, when he writeth up the people - בכתוב עמים bichthob ammim, in the register of the people. When he takes account of those who dwell in Jerusalem, he will particularly note those who were born in Zion.

This has an easy spiritual meaning. When God takes an account of all professing Christians, he will set apart those for inhabitants of the New Jerusalem who were born in Zion, who were born again, received a new nature, and were fitted for heaven.

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 adverted 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 that had his birth in Zion. Out of such would his own people be taken, and those thus born would have an honor which no one else would receive from him. He would not mark with any special approbation 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 in the main 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 early dedicated to God; and who have been trained up for his service. See the notes at Isaiah 44:3-5.

87:6 When - When God, the maker and governor of this city shall take a survey of all his citizens. It is an allusion to princes or governors of cities that use to write and keep a register of all their people.