Gal 3:16 (from a variant found on page 241 in "The Orthodox Corruption of Scripture", by Ehrman): "Now to Abraham -- of whom is the Messiah of Israel (Act 13:22-23; Heb 2:16) -- and his seed was the Promise made. It saith not, 'and to seeds', as of many; but as of one, 'and to thy seed'."
The emphasis of "one seed" over "many seeds" is to emphasize the necessitous progenitor, see Gen 15:2-4 & Gen 17:18-19.
There are four reasons why this verse is not saying the Messiah is the Promised Seed:
1. The Hebrew word for “blessed” in Gen 12:3 (also in Gen 18:17 & 28:14) is v'Nivrechu and according to the section under "Farming" in Yevamos 63, it means mixed or grafted. The Promise is: the absolved gentiles are those who are persuaded that they are the mixed seed of faithful Abraham (Gal 3:9).
2. The Promise is about "seeds, as of many” (Gen 22:16-18).
3. Joseph was the successor to the Birthright, not Judah (1Chr 5:1-2; Gen 49:22). Subsequently, that Birthright went to Joseph's second son, Ephraim, whose name means multiplicity of fruit (Gen 41:52; 48:19).
4. The origin of Yeshua was disputed (see The Virgin Birth
below), indeed it seemed ambiguous (Mat 1:23; Luk 1:34-35; Rom 1:3-4; 2Tim 2:8; Heb 7:14-15; Rev 5:5; 22:16; Luk 4:22). However in John Chapter 6 and verses 33 & 38 Yeshua said,” The Bread of Elohim is he who came down from Heaven, and resuscitates the lost sheep of the House of Israel, who are scattered throughout the world (see the Sidebar above right). For I came down from Heaven, not to do mine own will, but the will of Him that sent me”. The inference is to manna which was a seed that did not come through Ephraim but came from Heaven (Num 11:7-8).
The Promised Seed is Israel.
vs18 Now the conception of Yeshua the Messiah of Israel was
on this wise: When as his mother Mary was espoused to her
husband Joseph, before they lived together, she was found with
child by holy spirit (i.e. as promised, Luk 1:31).
vs19 Then Joseph her husband, being an innocent (naive), and not
willing to live with her, nor did he want to expose the fact
that he did not want to live with her (which would bring her to
shame), nor did he want to make her forbidden to marry until her
death (i.e. divorce her without a writ).
vs20 But while he thought on these things, behold, the angel
of YHVH appeared unto him in a dream, saying, Joseph, thou son
of David, fear not to cohabitate with Mary (thy wife): for that
which is conceived in her is by holy spirit (i.e. as promised).
vs21 And she shall bring forth a son, and thou shalt call his
name Yeshua (the English translation would be Josh -- short for
Joshua, which means YHVH saves): for YHVH shall save my people
from from our enemies, and from the hand of all that hate us
(Luk 1:71; Isa 11:11-14; Jer23:6a).
vs22-23 Now all this was done, that it might be fulfilled
which was spoken of YHVH by the prophet Isaiah, saying, "Behold,
a virgin shall conceive, and bear a son, and Judah shall
consider him to be Emmanuel, which being interpreted is, Elohim
is for us" (Isa 7:14).
Note: A virgin is a young woman who lives in her
father's house. She may be married, but if she has not moved
into the home of her husband she is still considered a virgin.
vs24-25 Then Joseph being raised from sleep did as the angel
of YHVH had bidden him, and cohabitated with his wife: But was
not intimate again till she had brought forth her firstborn son (the
whole point of identifying Mary as a virgin was to emphasize
that her child would be a firstborn, Luk 2:7): and he called his
vs31-33 And, behold, thou shalt conceive in thy womb, and
bring forth a son, and shalt call his name Yeshua. He shall be
great, and shall be called son of the Highest (Ex 13:2): and
YHVH Elohim shall give unto him the throne of his father David:
And he shall reign over the house of Jacob for ever; and of his
kingdom there shall be no end.
vs34 Then said Mary unto the angel, How shall this be, seeing
I have not been intimate with my husband?
vs35 (Ignoring her naiveness) the angel testified (from the
Heb. 'anah) and said
unto her, holy spirit shall come upon thee (Act 1:8), that
is the power of the Highest shall protect thee (Psalm 36:7; Jon
4:8): therefore also that holy thing which shall be born of thee
shall be called son of Elohim (because he will be the king of
Israel, vs 32-33).
Gal 3:14-15 That the blessing of Abraham will be fulfilled among the gentiles (see 'Who are the Gentiles' in the chapter entitled "What Must I Do to Be Safe?"), through Yeshua the Messiah of Israel; that we might receive the Spirit’s Promise (the promise to Abraham of a multitude of heirs) through faith. Brothers, let me make an analogy: no one makes deletions even to a human covenant that has been ratified, or makes additions to it.
Gal 3:17 And this I say, that the Covenant that was ratified by YHVH, the Torah, which was four hundred and thirty years later, does not void what was told to Abraham, that it should make the Promise of patrimony ineffectual.
Paul talked about the Promise preceding the Torah, in his letter to the Congregation of Israel in Rome.
Rom 4:13-16 The Promise, that Abraham should be the heir of hamon goyim (this Hebrew phrase means: a tumultuous and clamorous crowd of gentiles, Gen 17:4), was not to Abraham, or to his physical seed, through the Torah (the Promise was made 430 years before the Torah was even given), but through the righteousness of Abraham’s faith. For if they who are "of-the-Torah" (the descendants of Abraham who were circumcised in accordance to the Torah, Josh 5:4-7) be the sum total of Abraham’s heirs, Abraham’s faith is made void, and the Promise made to Abraham is ineffectual (because breaking the law of circumcision renders punishment as in Exo 4:24-26, yet where there is no law of circumcision that law has no effect). Therefore the Promise is by Abraham’s faith, that it might be by loving-kindness; to the end the Promise might be sure to all the seed; not to that only who is of-the-Torah but to that also who is of-the-faith-of-Abraham (or, descendants of Abraham in the same condition as he was, when righteousness was reckoned to him: uncircumcised); who is the father of us both (the Circumcision and the Uncircumcision).
The Promise to Abraham was a legacy or a birthright; an eternal possession into which someone is born. It was incumbent on the heirs to preserve this heritage. Certain sects of Judaism considered the legacy as their sole inheritance that could be used or disposed as they pleased. And thus, they sought to exclude the House of Israel from the Promise.
Gal 3:18-19 For if this patrimony is by means of Torah, it is no longer depends on a Promise; but YHVH gave this heritage to Abraham by Promise. Wherefore then serves the Torah? It was incorporated because of attempts to violate the Promise (the Greek word for "transgressions" is
parabasis, which means: a breach of something that was mutually accepted), until all the seed should be known of whom the Promise concerned (a process that will be fulfilled in the Resurrection, 1Pet 1:5).
Gal 3:21 "Therefore Torah is against YHVH’s Promises to Abraham about patrimony"? No, for if there had been a law which could have given life (a "law that concerned bodily descent", Heb 7:16, RSV), verily Abraham’s righteousness should have been by that law.