Augustine of Hippo

(Tr. xlvi. 1) Our Lord has acquainted us with two things which were obscure before; first, that He is the Door; and now again, that He is the Shepherd: I am the good Shepherd. (c. xlvii. 1, 3). Above He said that the shepherd entered by the door. If He is the Door, how doth He enter by Himself? Just as He knows the Father by Himself, and we by Him; so He enters into the fold by Himself, and we by Him. We enter by the door, because we preach Christ; Christ preaches Himself. A light shews both other things, and itself too. (Tr. xlvi. 5). There is but one Shepherd. For though the rulers of the Church, those who are her sons, and not hirelings, are shepherds, they are all members of that one Shepherd. (Tr. xlvii. 3). His office of Shepherd He hath permitted His members to bear. Peter is a shepherd, and all the other Apostles: all good Bishops are shepherds. But none of us calleth himself the door. He could not have added good, if there were not bad shepherds as well. They are thieves and robbers; or at least mercenaries.