Genealogy and Mission
or Blood versus Water
They answered and said to Him, “Abraham is our father.” Jesus said to them, “If you were Abraham’s children, you would do the works of Abraham… You are of your father the devil, and the desires of your father you want to do.” (John 8:39, 44)
The theme of seed and fruit, or genealogy and mission, runs throughout the Bible. Genealogy is entirely objective. Our heredity is a factor in which we have no choice. It is the tree of life. But the fruit of our lives, what we choose to do with that life, involves our volition. Volition is mission. “It’s not about the hand you are dealt; it’s about how you play it.”
Now, godly and ungodly decisions by individuals (beginning with Adam) do take on a corporate character. An idolatrous man was a man with a corrupt mission, but this would become a heredity in his culture. His children would be born into idolatry, just as Abraham’s sons were born into true worship. So there is genealogical (tribal) character and spiritual character.
Lot’s daughters’ godless decision brought Ammon and Moab into the world. Their spiritual adultery (lack of faith) led to incest, which led to idolatrous nations. One knew what to expect from an Ammonite or a Moabite.
But then God obviously takes great pleasure in violating those “genealogical” characters. Just as Israel was planted in anticipation of a good crop but brought forth thorns and thistles, so God can miraculously bring good fruit from the wild.
One could be a genealogical Canaanite but a spiritual Israelite (Tamar, Rahab, Ruth, Naaman the Syrian, the widow of Sidon). And one could also be a genealogical Israelite but become a spiritual Amalekite (Edom, Saul/Doeg, the Herods). It becomes clear that genealogy is not the end of the story, any more than raw flesh left on the altar is the end of the story.
The Old Testament uses genealogical “character” to signify spiritual character. Genealogical identities were given to teach us about spiritual things. Revelation uses many of the genealogical identities of the Old Testament to describe spiritual character. When the prophets (including Jesus and John) refer to Israel as Sodom, Egypt, Tyre and Babylon, they are name-calling. Israel was defying her Abrahamic heritage. The crop didn’t match the seed. Jesus referred to Naaman the faithful Syrian, and the faithful widow of Sidon, to shame the Jews. Paul’s ministry was about exactly that: believing Gentiles from the Covenantal wilderness would bring forth the fruit that was expected of the cultivated Land.
But the genealogical element ended with the New Covenant. The genealogical divide founded in Abraham’s circumcision came to an end with the destruction of the Temple. The entire world was moving from the age of seed to the age of fruit. It was part of the process of growing up.
Circumcision was about genealogy, seed. Baptism is about mission, fruit. Blood and water are both life-giving liquids, but they are different. One concerns genealogy; the other concerns mission. This is why Jesus was baptized as an adult, at the beginning of His earthly ministry. If baptism also concerns one’s parental origins, then Jesus could have been slain for the life of the world as an infant. But He wasn’t, and this highlights the very different character of the New Covenant and its membership.
Faith in Christ puts an end to our heredity. God takes great pleasure in violating our heredity with gospel, and that is what credobaptism is all about. This is not a genealogical change, or we would not still physically die. It is a missional change. Jesus makes this plain in his tirades against the Pharisees. He only speaks the words of the Father, He only does His Father’s business, because He carries the authority of the Father, the mission. In Jesus, Abrahamic genealogy and Abrahamic mission were united.
Jesus’ life before His baptism was about Adamic blood. (We are give only one account of His childhood because it sets a pattern for His life. After His Creation, the next major step is His Levitical Ascension, representing the Twelve. He is taken, missing like Enoch and Elijah, as Firstfruits.) 
His life after His baptism was about the works of the Spirit. His baptism was not a genealogical event, as was His circumcision. His baptism was missional. It was an investiture, an ordination. (It surprises me that my Federal Vision friends, many of whom make a big deal of the significance of ministerial robes, don’t see this more clearly.)
Adam was fully grown when he was given his mission, but he was not blameless when it came to his investiture, so he was robed in blood. Genealogy and mission were divided. But Jesus took mankind from the Tree of Life (genealogy/heredity) to the Tree of the Knowledge of Good and Evil (mission/career), from seed to fruit, from Alpha to Omega, from childhood to maturity.
Paedobaptism drags the nature of the genealogical Old Covenant into the missional New Covenant. Some take the “threshing” process of the first century and apply it to the Church so they can keep on baptizing tares. But the threshing process described in the New Testament was a first century event. Jesus was bringing Israel’s purpose to an end. To use these images indiscriminately now is to rip them out of their historical context. The apostles were dividing, with the sword of the Gospel, between the merely genealogical seed of Abraham and Jew/Gentile spiritual fruit.
One could be Jewish and not believe. One cannot be a Christian and not believe. We are not of the physical seed of Abraham. To maintain a genealogical Covenant, paedobaptism assumes some kind of physical “Christian seed.” Not only is there no support for this in Scripture, it rides against everything that’s going on in the New Testament. John 8:37 cannot be applied to anyone post AD70.
One was connected to Israel by blood. One is connected to Christ, the true Israel, by Spirit. That means if one is not regenerate one is not connected. The New Covenant is about a different kind of life, one that is not merely objective, but both objective and subjective, that is, missional. God calls and the Christian responds.
The “Covenant connection” assumed in paedobaptism is actually enjoyed by everyone on earth. It is the claim of Jesus upon the lives of all men of all nations. Certainly, the Church must excommunicate those who have made a false profession. But they were baptized upon that profession, not their heredity, and they are excommunicated when that profession proves false.
The Old Testament is about seed. The New Testament is about fruit. The Covenants are related, but fundamentally different. Fruit is not seed, and fruit begins with confession/profession. One joins the New Covenant people of God not because one has the same flesh, but because one is a man after God’s heart—a true representative.
 The Avatar movie contains the same process. Jake is “chosen” by the creator (head) then “chosen” by the people (body). See James Cameron, Bible Avatar.