He appointed twelve—designating them apostles —that they might be with him and that he might send them out to preach.  Mark 3:14

It is no coincidence that Jesus chose twelve apostles, the same number as the twelve tribes of Israel that come from the twelve sons of Jacob (renamed Israel).

The apostles were invited, saying that one's invitation into this new group is not by birth or heritage, but by choice.  Jews are Jews by birth.  Christians are Christians by accepting the invitation to follow.

The apostles formed a newly organized group that would take the foundation of what the twelve tribes started and took it out into the world.  It was no longer localized to a region, but spread globally.

The tribes were shepherds who lead a designated group of sheep around from place to place.  The apostles were (mostly) fishermen who throw out nets and grab large groups of fish, of all kinds.  The tribes focused on their own people.  The apostles focused on Jews and Gentiles, those outside the Jewish region.

Jesus was saying by choosing twelve apostles that he was regrouping what the Jewish faith started and turning it into a more globalized movement.

The last book of the Bible, Revelation, pictures heaven with acknowledgements of what both groups did.  Both are important.

It had a great, high wall with twelve gates, and with twelve angels at the gates. On the gates were written the names of the twelve tribes of Israel. There were three gates on the east, three on the north, three on the south and three on the west. The wall of the city had twelve foundations, and on them were the names of the twelve apostles of the Lamb.  Revelation 21:12-14