It's not Hagar. Hagar is the tare. It's Sarah, the line of the Promise.
Yes, Sarah the freewoman gives birth to Isaac the child of promise. And we, like Isaac, are children of promise, born after the spirit.
23 Howbeit the son by the handmaid is born after the flesh; but the son by the freewoman is born through promise.
24 Which things contain an allegory: for these women are two covenants; one from mount Sinai, bearing children unto bondage, which is Hagar.
25 Now this Hagar is mount Sinai in Arabia and answereth to the Jerusalem that now is: for she is in bondage with her children.
26 But the Jerusalem that is above is free, which is our mother.
27 For it is written, Rejoice, thou barren that bearest not; Break forth and cry, thou that travailest not: For more are the children of the desolate than of her that hath the husband.
28 Now we, brethren, as Isaac was, are children of promise.
29 But as then he that was born after the flesh persecuted him that was born after the Spirit, so also it is now. Gal 4
5 And she was delivered of a son, a man child, who is to rule all the nations with a rod of iron: and her child was caught up unto God, and unto his throne.
17 And the dragon waxed wroth with the woman, and went away to make war with the rest of her seed, that keep the commandments of God, and hold the testimony of Jesus: Rev 12