Ye are clean, but not all. For He knew who should betray Him; therefore said He, ye are not all clean (John 13:10,11).
Our Lord did not make a terrible mistake in selecting Judas to be one of the twelve disciples. It was neither an accident nor a blunder. There were very definite reasons for Judas being in this select group; even though he was unclean (unsaved) and referred to as the son of perdition (John 17:12).
At the Passover before His death, Jesus made this startling statement concerning Judas: The Son of man indeed goeth, as it is written of Him: but woe to that man by whom the Son of man is betrayed! good were it for that man if he had never been born (Mark 14:21). So, why Judas? The betrayal of Judas gave dramatic evidence to the fact of the deity of Christ. Jesus said, Now I tell you before it come, that, when it is come to pass, ye may believe that I am He (John 13:19). He is not in the actual Greek text, and thus can be translated simply, I am. I AM is the Old Testament name, Jehovah. He predicted the betrayal and only God can do that. Judas betrayal was a fulfillment of Scripture. In John 13:18, Jesus quotes Psalm 41:9: He that eateth bread with me hath lifted up his heel against me. As Ahithophel turned against David and eventually hanged himself, even so, Judas would turn against Christ and die in the same manner. Judas would give vital testimony to the fact of Christs innocence. When he saw that he was condemned, repented himself, and brought again the thirty pieces of silver to the chief priests and elders, Saying, I have sinned in that I have betrayed the innocent blood (Matthew 27:3,4). He gave true witness as to Christs character and person.
Judas went out into a night that never ended (John 13:30), because he never truly received Christ into his life. NPS