--2 Cor 4:7-15
Christ himself chose the apostles and gave them a share in his mission and authority. Raised to the Father's right hand, he has not forsaken his flock but he keeps it under his constant protection through the apostles, and guides it still through these same pastors who continue his work today. Thus, it is Christ whose gift it is that some be apostles, others pastors. He continues to act through the bishops.
-- CCC 1575