What is the main issue behind the blood curse that God gave to Jehoachin? Why is this a great witnessing tool when speaking to a Jewish friend?

Jewish friend, try a Catholic friend. We were talking about Easter and I said Jesus’ brother James didn't believe he (Jesus) was the Messiah until after the resurrection. I was quickly informed that Jesus had no brothers by Mary and Joseph only spiritual brother. From bad to worse as I said Mary and Joseph had a number of children and I added that Mary was not the product of an immaculate concept. I was informed that Mary died a virgin. I never had a chance to point out that Mary would not be of David line if not for her father Heli. We’re good friends so we agreed to disagree; however, perhaps I have her thinking. So I’ll save our discussion about the blood curse on Jehoachin and Jesus descending from King David’s son Nathan through Heli the father of Mary for another time.

Although I had written on this subject in PRO501 after today’s discussion a re-visit is timely.

It is always amazing how God sets in motion an event that will have great important at a later date. King Jeconiah, a descendant of King David through Solomon promoted idol worship and evil deeds which really out-raged our righteous God. So God pronounced a blood curse on the line of Jehoiachin, saying that none of his descendants would ever sit on the throne of David. This meant that no Messiah could come from a male in the line of David as there was now a blood curse pronounced on the only males left in the royal line.

Centuries before the daughters of Zelophehad had no brother for their father to leave his goods and property to. So they petitioned Moses Numbers 27: 4, “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.” Moses took their petition before the Lord. And the Lord said, Numbers 27: 8, “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.” When the daughter married her father would adopt his son-in-law as his son.

Thus God solved the future problem of the blood curse on Jeconiah and all his sons. Jesus’ mother Mary had no brother so her father could adopt her husband Joseph, the legal father of Jesus. Joseph was in the line of King David but was tainted by the blood curse. Mary was in the line of Kind David through his son Nathan. Mary was the biological mother of Jesus born of her “seed” as predicted thousands of years before in the Garden of Eden.
If I were trying to convince a Jewish friend I would use this line of reasoning and pray I was more convincing than I was with my Catholic friend.