First, we should mention that those reverend Apostles had been called for their mission by Jesus Christ himself. He
is the One who said to them:" You did not choose Me, but I chose you
and appointed you that you should go and bear fruit, and that your
fruit should remain, that whatever you ask the Father in My name He may
give you" (Jn15:16)
And Jesus Christ also said to them after the Resurrection" As the Father has sent Me, I also send you"(Jn20:21).
gracious it is that God's servants are called to the service by God
Himself. St. Paul the Apostle said in his Epistle to the Hebrews "And
no man takes this honor to himself, but he who is called by God, just
as Aaron was"(Heb5:4).