Romans 1:1-5 KJV
Paul, a servant of Jesus Christ, called to be an apostle, separated unto the gospel of God,  (Which he had promised afore by his prophets in the holy scriptures,)  Concerning his Son Jesus Christ our Lord, which was made of the seed of David according to the flesh;  And declared to be the Son of God with power, according to the spirit of holiness, by the resurrection from the dead:  By whom we have received grace and apostleship, for obedience to the faith among all nations, for his name:
They received apostleship FOR obedience to the faith..
Its like God is saying that he'd only have chosen these men as apostleship because he knew they'd be obedient to the calling!
Especially if you look back up at the part in version 2 about how this was fulfilling prophecy!