Jesus answered them, Have not I chosen you Twelve, and one of you is a devil? V. 71. He spake of Judas Iscariot, the son of Simon; for he it was that should betray Him, being one of the Twelve.
The answer of Jesus upon the glorious confession of Peter was charged with deep feeling and carried a warning, especially to one of the Twelve. For although Jesus had chosen them all in the same way and with the same seriousness, yet one of them was a devil at heart, and was merely hiding his denial and hostility under the hypocritical mask of loyalty. That was Judas Iscariot. In him the devil lived and had free play, he was Satan's willing victim and tool.
That is a truly devilish crime, if a disciple, a believer, such as Judas was, that actually acknowledges Jesus as the Christ and has had many an experience in his Christian life, finally gives up his belief in the Savior and becomes an apostate. The example of Judas serves as an earnest warning to watch and to pray, lest faith be taken away and we commit the sin of Judas, betray our Lord and Savior.