I am sure you have all seen references to the usual Christmas story on the various blogs you read so I thought I would tie some things together
Leviticus 25:25; If thy brother be waxen poor, and hath sold away [some] of his possession, and if any of his kin come to redeem it, then shall he redeem that which his brother sold
25:47-49 And if a sojourner or stranger wax rich by thee, and thy brother [that dwelleth] by him wax poor, and sell himself unto the stranger [or] sojourner by thee, or to the stock of the stranger’s family:
After that he is sold he may be redeemed again; one of his brethren may redeem him:
Either his uncle, or his uncle’s son, may redeem him, or [any] that is nigh of kin unto him of his family may redeem him; or if he be able, he may redeem himself.
We see here that only a kinsman redeemer would be able to redeem us from the debt of sin. And as all have sinned and fallen short of the glory of G-d, and as that debt is not one we could ever repay, it is only through a kinsman who is both willing and able to repay the debt that our ransom could be paid. It is also important that the Christ indeed be a human and therefore our kin, that He might buy us our freedom.
The genealogy in Matthew gives us the lineage of Joseph which traces back through King David of whom the Meshiach Nagid was to come. But there is a problem with this. Joseph was technically in line for the throne should one ever come back, but was under the curse placed upon his forefather (and King) Jechoniah which was pronounced by the Prophet Jeremiah
Thus saith the LORD, Write ye this man childless, a man [that] shall not prosper in his days: for no man of his seed shall prosper, sitting upon the throne of David, and ruling any more in Judah.
So clearly no son of Joseph could rule upon that throne. So lets look at the genealogy given in Luke 3:23-38 which makes clear the lineage of Mary through King David, but not through Jechoniah. So Mary is of a good lineage, but she is a woman and cannot pass along a birthright such as one to the throne. In fact, as the lineage is traced through the father she had nothing to offer in way of birthright. So what gave Mary this right? It is because of the law laid out in Numbers 27 as shown below.
Number 27:1-8 Then came the daughters of Zelophehad, the son of Hepher, the son of Gilead, the son of Machir, the son of Manasseh, of the families of Manasseh the son of Joseph: and these [are] the names of his daughters; Mahlah, Noah, and Hoglah, and Milcah, and Tirzah. And they stood before Moses, and before Eleazar the priest, and before the princes and all the congregation, [by] the door of the tabernacle of the congregation, saying, Our father died in the wilderness, and he was not in the company of them that gathered themselves together against the LORD in the company of Korah; but died in his own sin, and had no sons. Why should the name of our father be done away from among his family, because he hath no son? Give unto us [therefore] a possession among the brethren of our father.
And Moses brought their cause before the LORD. And the LORD spake unto Moses, saying, The daughters of Zelophehad speak right: thou shalt surely give them a possession of an inheritance among their father’s brethren; and thou shalt cause the inheritance of their father to pass unto them. And thou shalt speak unto the children of Israel, saying, If a man die, and have no son, then ye shall cause his inheritance to pass unto his daughter.
So from Mary’s side the Messiah is of the seed of David, and from His legal,adoptive father Joseph he gains a legal claim to the throne of Israel, but without the accompanying curse that ended the line of kings so long ago. All this so that we may be reconciled to a gracious G-d who created the universe and set the stars in motion, and yet cares enough about mankind that He sent His Son here to die, to shed His blood in a horrific and painful manner so that lowly man could stand in the presence of the Almighty.