Why did Jesus tell Judas he would be the head of one of the twelve tribes
if Judas was going to betray him? Who were the Twelve who saw the risen
Christ in Paul’s account of the resurrection. If Judas was dead how could
he be one of the “twelve” who saw Christ.

Jesus did not specifically tell Judas he would be head of a
tribe. What did happen is that Jesus addressed the twelve apostles,
telling them “I tell you the truth, at the renewal of all things, when the
Son of Man sits on his glorious throne, you who have followed me will also
sit on twelve thrones, judging the twelve tribes of Israel.” (Matthew
19:28) God used the twelve apostles as a prophetic parallel to the twelve
tribes of Israel in several ways. Revelation 21:12-14 describes the
twelve tribes and the twelve apostles in similar symbolic language. When
Jesus told the apostles that they would reign with him, he was speaking to
them as a group. After he betrayed Jesus and killed himself, Judas was
replaced by Matthias, as described in Acts 1:18-26. God was able to
fulfill the statement in Matthew 19:28 despite Judas’ betrayal. If one
thinks about the scene in Matthew 19 (I am assuming this scene is what you
are referring to in your question), it would have been very awkward for
Jesus to say “the twelve of you, except for Judas, who is going to betray
me, will reign with me on twelve thrones.” Jesus knew all along who would
betray him, but it was all part of God’s plan, so Jesus did not repudiate
Judas publicly until the night he was betrayed. All this shows us two
things. 1. Jesus knew all along what would happen to him and he willingly
gave himself to die for our sins. and 2. God is in control of human
events.

This answers your second and third questions. If one looks at
Acts 1:18-26, those who chose the replacement in “the Twelve” for Judas
were specific that the person had to be a witness of the Resurrection.
Because Matthias was a witness of the ministry and the resurrection of
Jesus, Paul’s statement in 1 Corinthians 15 is true.

John Oakes, PhD