The Biblical percentages are such that one out of every twelve disciples is a Judas. On average, there is a Judas among every twelve people in the life of a real Christian. This being the case, it may be wise to limit your friends to eleven people. But really, the Judas problem exists, and it will never go away. It is one of those things we must be aware of, but keep on the back burner. Eleven out of twelve, on average, are on your side and will not betray you, and this must always be our focus.
The Lord knew the heart of Judas. He knew He had chosen “the son of perdition” as one of His original twelve. David prophesied of this man:
All who hate me whisper together against me; against me they devise my hurt, saying, “A wicked thing is poured out upon him, that when he lies down, he will not rise up again.” Even my close friend in whom I trusted, who ate my bread, has lifted up his heel against me. [Psalm 41:7-9]
Yet Judas was in no way predestined to perform his dirty deed. He was not created to be a jerk. He chose to be a jerk. It seems that the other apostles did not suspect him. None of them knew who the traitor was at the Last Supper, for example. It is apparent that Judas hid himself very well.
He was the holder of the money bag. And he repeatedly stole from it. Imagine that. He was routinely stealing the money given for the work of God. The only one who knew this, apparently, was the Lord. Maybe the others did know it. Maybe they knew Judas was a thief but did not know he would be a traitor. There was something not quite right about this man. Each of the original apostles was messed up in some way. They each had their personality quirks and sin problems. Except for John, they all eventually ran off and/or denied the Lord after His arrest.
But they returned. Their hearts were right. They simply did not understand. They were afraid. But Judas was a betraying thief with his own agenda. He was not on the same page with the Lord or the others. He was listening to a different radio station. He was getting his information from a different source. At the time of the end, his increasingly cozy relationship with the devil himself caused the two to come into perfect union. It was a spiritual marriage. The devil entered into Judas and the two became one. Whoa.
It had been building for some time. At whatever point it commenced we do not know for sure, but Judas Iscariot had decided he would either take back his heart from the Lord or never give it fully to Him. It could be that he, like the others, could only perceive the popular notion of the Messiah as a conquering hero. He noticed early on that the Lord Jesus did not seem to fit this role. He thus held back his heart. The others thought the same thing generally, but gave their hearts to the Lord anyway. They overcame anything that might have held them back, and each of them sided with the Lord 100%. They still messed up from time to time, but their hearts were right.
Not so with Judas. And not so with any possible unknown Judas in your life. The Lord never advocated being suspicious of others, though. Suspicion and love do not go together. The best Scriptural advice concerning how to best approach this subject, straight from the Lord’s teachings, is probably the following:
“Behold, I send you out as sheep in the midst of wolves; so be shrewd as serpents and innocent as doves.” [Matthew 10:16]
The Lord knew about Judas but carried the knowledge well. It takes a certain strength to do this, a great strength. He loved Judas to the very end and knew there was always hope on the one hand, but was aware of his eventual fate on the other. He never let this knowledge or the various actions of Judas affect His mission or relationship with others, however. He never even fought against the actions of Judas, but allowed them to play out as part of a plan. One solution to this is that it was already predetermined there must be a traitor, because Satan would counter the Lord’s ministry with betrayal. Under the devil’s overall tempting influence upon everyone close to the Lord, Judas Iscariot was the one who gave in to temptation and chose the role.
Let love be without hypocrisy. Abhor what is evil; cling to what is good. Be devoted to one another in brotherly love; give preference to one another in honor; not lagging behind in diligence, fervent in spirit, serving the Lord; rejoicing in hope, persevering in tribulation, devoted to prayer, contributing to the needs of the saints, practicing hospitality. Bless those who persecute you; bless and do not curse. Rejoice with those who rejoice, and weep with those who weep. Be of the same mind toward one another; do not be haughty in mind, but associate with the lowly. Do not be wise in your own estimation. Never pay back evil for evil to anyone. Respect what is right in the sight of all men. If possible, so far as it depends on you, be at peace with all men. [Romans 12:9-18] 
© 2011 by RJ Dawson. All Rights Reserved.
 Unless otherwise noted all Scriptures are taken from the New American Standard Bible, © 1960, 1963, 1968, 1971, 1972, 1973, 1975, 1977, 1995 by The Lockman Foundation. Used by permission.