Galatians
Galatians 4:26
"But Jerusalem which is above is free, which is the mother of us all," (Galatians 4:26 KJV).
Here, Paul tells us that Jerusalem is our mother, but what does this mean? Paul is making a contrast here using an Old Testament passage. The contrast begins with speaking of the two wives of Abraham. He had two sons, one of a servant, and one by his actual wife (Galatians 4:22-23). Paul uses this to explain how Jerusalem was in his day (Galatians 4:24-30). "Now this Hagar is Mount Sinai in Arabia and corresponds to the present Jerusalem, for she is in slavery with her children. But the Jerusalem above is free; she is our mother," (Galatians 4:25-26 NASB1995). The present inhabitants of Jerusalem are in a sense slaves while the Jerusalem above is free. Paul is making the point that the new Jerusalem is free, one that Christians are a part of (Galatians 4:31). See Isaiah 65:17-25 & Revelation 21:2.
Christ set us free from the Old Covenant to the New: "It was for freedom that Christ set us free; therefore keep standing firm and do not be subject again to a yoke of slavery. Behold I, Paul, say to you that if you receive circumcision, Christ will be of no benefit to you," (Galatians 5:1-2 NASB1995).
The New Jerusalem being the mother of us is as if to say as "Many Jewish texts in Paul's day reinforced the Old Testament hope of a new Jerusalem, often speaking of a heavenly Jerusalem that would come down to earth. These texts also sometimes spoke of Jerusalem (present or future) as "our mother (e.g., 4 Ezra 10:7; cf. Is 66:7-10 with 65:17-18). Others spoke of the Jerusalem "above" (4 Baruch 5:35). (Gentiles often spoke of earth as a "mother," and the mother goddess was particularly popular in Phrygian Galatia; but Gentiles also spoke of their "mother city" and would understand that Jerusalem was Judeans' mother city.) Because Judaism associated the Messiah and the Spirit with the end time, Paul would naturally identify followers of the Messiah Jesus with the future Jerusalem rather than with the present one. ... the restoration of God's people in terms of Jerusalem as a mother giving birth (relevant for Gal 4:26)," (Keener 536). (C.f. Crossway 2253).
The New Jerusalem will be, in some sense, our mother city, the one where we will reside.
References:
New American Standard Bible®, Copyright © 1960, 1971, 1977, 1995 by The Lockman Foundation. All rights reserved.
ESV Study Bible. United States, Crossway, 2008.
Keener, Craig S. The IVP Bible Background Commentary: New Testament, 2nd Edition. United Kingdom, InterVarsity Press, 2014.