John 10:6

(Tr. xlv. 10. ct seq.) But here is a difficulty. Sometimes they who are not sheep hear Christ's voice; for Judas heard, who was a wolf. And sometimes the sheep hear Him not; for they who crucified Christ heard not; yet some of them were His sheep. You will say, While they did not hear, they were not sheep; the voice, when they heard it, changed them from wolves to sheep. Still I am disturbed by the Lord's rebuke to the shepherds in Ezekiel, Neither have ye brought again that which strayed. (Ezek. 34:4) He calls it a stray sheep, but yet a sheep all the while; though, if it strayed, it could not have heard the voice of the Shepherd, but the voice of a stranger. What I say then is this; The Lord knoweth them that are His. (2 Tim. 2:19) He knoweth the foreknown, he knoweth the predestinated. They are the sheep: for a time they know not themselves, but the Shepherd knows them; for many sheep are without the fold, many wolves within. He speaks then of the predestinated. And now the difficulty is solved. The sheep do hear the Shepherd's voice, and they only. When is that? It is when that voice saith, He that endureth to the end shall be saved. (Mat. 10:32) This speech His own hear, the alien hear not. (ut sup.) Our Lord feedeth by plain words, exerciseth by obscure. For when two persons, one godly, the other ungodly, hear the words of the Gospel, and they happen to be such that neither can understand them; one says, What He saith is true and good, but we do not understand it: the other says, It is not worth attending to. The former, in faith, knocks, yea, and, if he continue to knock, it shall be opened unto him. The latter shall hear the words in Isaiah, If ye will not believe, surely ye shall not be established. (Isa. 7:9)