1) Maimonides devotes much of the "Guide for the Perplexed" to the fundamental idea that God is incorporeal, meaning that He assumes no physical form. God is Eternal, above time. He is Infinite, beyond space. He cannot be born, and cannot die. Saying that God assumes human form makes God small, diminishing both His unity and His divinity. As the Torah says: "God is not a mortal" (Numbers 23:19).
2) In response, it is claimed that Joseph adopted Jesus, and passed on his genealogy via adoption. There are two problems with this claim:
a) There is no Biblical basis for the idea of a father passing on his tribal line by adoption. A priest who adopts a son from another tribe cannot make him a priest by adoption;
b) Joseph could never pass on by adoption that which he doesn't have. Because Joseph descended from Jeconiah (Matthew 1:11) he fell under the curse of that king that none of his descendants could ever sit as king upon the throne of David. (Jeremiah 22:30; 36:30)
To answer this difficult problem, apologists claim that Jesus traces himself back to King David through his mother Mary, who allegedly descends from David, as shown in the third chapter of Luke. There are four basic problems with this claim:
a) There is no evidence that Mary descends from David. The third chapter of Luke traces Joseph's genealogy, not Mary's.
b) Even if Mary can trace herself back to David, that doesn't help Jesus, since tribal affiliation goes only through the father, not mother. Cf. Numbers 1:18; Ezra 2:59.
c) Even if family line could go through the mother, Mary was not from a legitimate Messianic family. According to the Bible, the Messiah must be a descendent of David through his son Solomon (II Samuel 7:14; I Chronicles 17:11-14, 22:9-10, 28:4-6). The third chapter of Luke is irrelevant to this discussion because it describes lineage of David's son Nathan, not Solomon. (Luke 3:31)
d) Luke 3:27 lists Shealtiel and Zerubbabel in his genealogy. These two also appear in Matthew 1:12 as descendants of the cursed Jeconiah. If Mary descends from them, it would also disqualify her from being a Messianic progenitor.
