The Almighty is introduced as making a revelation to the psalmist. He will cause the Gentiles to flock into his Church, even those who have been hitherto the most bitter enemies of Israel (Psalms 87:4), and will place these strangers on a par with such as have belonged to his Church from their birth (Psalms 87:4, Psalms 87:5, Psalms 87:6), admitting them to every blessing and every privilege.
The Church, thus augmented, shall be taken under his own protection, and "established," or placed on a sure footing, forever. Compare our Lord's promise to St. Peter," On this rock will I build my Church, and the gates of hell shall not prevail against it" (Matthew 16:18).