I remember one time as a younger student at a Christian university in South Carolina, we were asked if the virgin birth was necessary for salvation. I, unlike most of the younger students in the class, responded with an emphatic yes. The professor then proceeded to explain why it was not by pointing out Romans 8:9-10 to prove that only faith was required. I then proceeded to remind him, I was a bit older than most of the students in the class, that without the virgin birth, Romans 8:9-10 would be irrelevant, for if Christ was not born of a virgin, then he was conceived in sin just like the rest of us.
This backdrop brings me to the texts at hand today: the genealogies of Matthew 1:1-16 and Luke 3:23-38. Matthew is the genealogy of Jesus through Joseph. Luke is the genealogy of Jesus through Mary. A careful study of these two genealogies would reveal that they are identical except in two points: 1. the genealogy of Joseph works forward and Mary’s works backward, and 2. they differ from King David on. In Matthew 1:6, we discover that the genealogy works from David through Solomon to Joseph, while in Luke 3:31, the genealogy works from one of David's other sons, Nathan, to Mary.
Why is this important? - Because it proves the necessity of the virgin birth. In Joseph’s genealogy through Solomon, it goes through a king by the name of Jeconiah (or Coniah), while Mary's does not. In Jeremiah 22:24-30, it says, "As I live, saith the LORD, though Coniah the son of Jehoiakim king of Judah were the signet upon my right hand, yet would I pluck thee thence; And I will give thee into the hand of them that seek thy life, and into the hand of them whose face thou fearest, even into the hand of Nebuchadrezzar king of Babylon, and into the hand of the Chaldeans. And I will cast thee out, and thy mother that bare thee, into another country, where ye were not born; and there shall ye die. But to the land whereunto they desire to return, thither shall they not return. Is this man Coniah a despised broken idol? is he a vessel wherein is no pleasure? wherefore are they cast out, he and his seed, and are cast into a land which they know not? O earth, earth, earth, hear the word of the LORD. 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."
In the end, if Joseph were truly the biological father of Jesus, he would not be qualified to sit on the throne of David because of this curse. That is why the Bible says in Isaiah 7:14, “Therefore the Lord himself shall give you a sign; Behold, a virgin shall conceive, and bear a son, and shall call his name Immanuel.” No, the virgin birth is not optional.