I read Psalm 87 this morning. What a glorious picture of the Gospel as the Gentiles are included in Zion! Verse 4 reads, "Among those who know me I mention Rahab and Babylon; behold, Philistia and Tyre, with Cush — 'This one was born there,' they say."
In a commentary I read along of the Psalms entitled "Christ's Psalms, Our Psalms", the writer mentioned that this undoubtedly speaks of the reality of the new birth in our regeneration by the Spirit. It also reminds me of Phil. 3:20-21, "But our citizenship is in heaven, and from it we await a Savior, the Lord Jesus Christ, who will transform our lowly body to be like his glorious body, by the power that enables him even to subject all things to himself."
Praise God that Christ has broken down all the barriers that separate us from God and one another. In Christ, Gentiles like us have our citizenship in Zion–the one holy catholic (universal) church!