29 Moreover, bishops have a very heavy burden in consequence of the difficulties of the times; and heavier still is their anxiety for the salvation of the flock committed to their care: "For they watch as being to render an account of your souls" ( Heb . xiii. 17). Are not, then, they to be termed cruel who, by the refusal of the obedience which is due, increase that burden and its bitterness? "For this is not expedient for you" ( Heb . xiii. 17), the Apostle would say to them, and that, because "the Church is a people united to its bishop, a flock which adheres to its pastor" (St. Cyprian: Ep. 66 [ al . 69]), whence it follows that he is not with the Church who is not with the bishop.
Source: Ad Beatissimi Apostolorum (Vatican.va)