Jesus was ordaining them for His ministry.

Matthew 10:2-4 "Now the names of the
twelve apostles are these;
The first, Simon, who is called Peter,
and Andrew his brother;
James the son of Zebedee,
and John his brother;
Philip, and Bartholomew;
Thomas, and Matthew the publican;
James the son of Alphaeus,
and Lebbaeus, whose surname was Thaddaeus;
Simon the Canaanite,
and Judas Iscariot, who also betrayed him."

This is how they are listed in Matthew when
Jesus called them. They didn't necessarily
go out in this order as many times they were
sent two by two.