Psalms 87:6 - Joseph Benson’s Commentary on the Old and New Testaments

The Lord, shall count, when he writeth up the people In the book of life, that register of heaven, kept by God himself, in which men's names are entered, not as born of flesh and blood, by the will of man, but as born of the Spirit, by the will of God; that this man was born there By a spiritual birth, and therefore, that he is a genuine and free citizen of Zion, that is, God shall esteem such a one, though of Gentile race, a true member of his church, when he takes a particular account and survey of all his citizens and subjects. The psalmist alludes to the custom of princes or governors of cities, who used to write and preserve a register of all their people. Observe, reader, the birth here spoken of, the second birth, the birth from above, not of water merely, but of the Spirit, producing love to God, deadness to the world, and holiness of heart and life, (1Jn 4:7; 1 John 5:4; 1Jn 3:9; 1 John 5:18,) is the only birth we ought to value ourselves upon, because this alone gives us a title to “the inheritance of the saints in light.” Such, and only such, are written among the living in Jerusalem, Isaiah 4:3. Or, written in the writing of the house of Israel, Ezekiel 13:9. Or, in the language of the New Testament, such only have their names in the Lamb's book of life, Philippians 4:3. And we know the consequence of not being found written there: see Revelation 20:15.