Was Isaac born of the "spirit" like Christ was?

[InChristAlways]

Hi forum,
Was Isaac born of the "spirit" without union between Sarah and Abraham? If so, was this symbolizing also that the "HEIR" from Abraham's "own body" would also be born through the "spirit" as Christ was?
The reason I ask this, is because I think Israel believes the messiah will be born through "regular union" between a husband and wife and would like to ask jews why they believe that the "messiah" will come through the "normal" way and not by the "spirit"?
The rulers of Jerusalem("Hagar") in the first century persecuted those saints of the faith and spirit of Christ(Isaac) and why even the descendants of Ishmael that come to Christ are "God's chosen" and are blessed through Abraham through Christ and those not of Christ are "cursed" and cutoff from the "Jerusalem above".
One other question, why was Sarai and Abram names changed in gene 17? What did that signify? Thanks and God bless.
(see also this thread http://www.theologyweb.com/forum/sho...843#post871843

gala 4:21 Tell me, ye who are willing to be under law, the law do ye not hear? 22 for it hath been written, that Abraham had two sons, one by the maid-servant, and one by the free-woman, 23 but he who [is] of the maid-servant, according to flesh hath been, and he who [is] of the free-woman, through the promise; 24 which things are allegorized, for these are the two covenants: one, indeed, from mount Sinai, to servitude bringing forth, which is Hagar; 25 for this Hagar is mount Sinai in Arabia, and doth correspond to the Jerusalem that now [is], and is in servitude with her children, 26 and the Jerusalem above is the free-woman, which is mother of us all,27 for it hath been written, `Rejoice, O barren, who art not bearing; break forth and cry, thou who art not travailing, because many [are] the children of the desolate--more than of her having the husband.' 28 And we, brethren, as Isaac, are children of promise, 29 but as then he who was born according to the flesh did persecute him according to the spirit, so also now; 30 but what saith the Writing? `Cast forth the maid-servant and her son, for the son of the maid-servant may not be heir with the son of the free-woman;' 31 then, brethren, we are not a maid-servant's children, but the free-woman's.

God tells Abram his seed will be of the number of the stars, and this is BEFORE Isaac and Ishmael are born. The "heir" would be the messiah Christ and those descendants born of Abram would be the inheritors of the "land" above, the New Jerusalem as quoted in galatians 4, that includes descendants of both Ishmael and Isaac and all those of the faith of the "HEIR" and the Heir's Father, Abraham.
Isaac was said to be born of the "spirit" just as Christ was born of the "spirit" and this appears to prove that Christ was not to come though a "normal union" by a man and wife like Ishmael was(symbolical). Was Isaac born of union of Abram and Sarai and why were both their names changed?.

gene 15:3 And Abram said--Lo, to me, hast thou not given seed,--And lo! a son of my household, is mine heir! 4 And lo! the word of Yahweh [came] unto him, saying, This one, shall not be thine heir; But, one who cometh forth of thy body--he, shall be thine heir. 5 And he brought him forth abroad, and said--Look steadfastly, I pray thee, towards the heavens, and number the stars, if thou be able to number, them, And he said to him, Thus, shall be thy seed. 6 And he had faith in Yahweh,--so he reckoned it to him, as righteousness.

gene 17:4 As for me, lo! my covenant is with thee,--So shalt thou become--father of a multitude of nations; 5 And thy name shall no more be called Abram,--but thy name shall become Abraham, for, father of a multitude of nations, have I appointed thee; 6 And I will make thee fruitful, exceedingly, and grant thee to be nations,--Yea, kings, out of thee, shall come forth; 7 And I will confirm my covenant betwixt me and thee, and thy seed after thee to their generations, for an age-abiding covenant,--to become to thee a God, and to thy seed after thee;........... 15 And God said unto Abraham, As for Sarai thy wife, thou shalt not call her name, Sarai,--but, Sarah, is her name; 16 And I will bless her, yea moreover will give--from her--to thee, a son,--And I will bless her, and she shall become nations. Kings of peoples, from her, shall arise.