Wherefore come out from among them, and be ye separate, saith the Lord, and touch not the unclean thing; and I will receive you, 2 Corinthians 6:17
There are those, like Judas who look like Christians at a distance but the closer you get the further they shown to be from Christ. Remember when Judas rebuked Martha for anointing Jesus with the oil? He feigned sympathy for the poor but the Holy Spirit let us know that he cared not for the poor but for the money for he was a thief.
They profess that they know God; but in works they deny him, being abominable, and disobedient, and unto every good work reprobate. Titus 1:16
Jesus even let his disciples know that many would call him LORD but in the end they would be cast away, never known by God.
Matthew 7:21Not every one that saith unto me, Lord, Lord, shall enter into the kingdom of heaven; but he that doeth the will of my Father which is in heaven.
22Many will say to me in that day, Lord, Lord, have we not prophesied in thy name? and in thy name have cast out devils? and in thy name done many wonderful works?
23And then will I profess unto them, I never knew you: depart from me, ye that work iniquity.
Paul warned of these who have a form of godliness:
1This know also, that in the last days perilous times shall come.
2For men shall be lovers of their own selves, covetous, boasters, proud, blasphemers, disobedient to parents, unthankful, unholy,
3Without natural affection, trucebreakers, false accusers, incontinent, fierce, despisers of those that are good,
4Traitors, heady, highminded, lovers of pleasures more than lovers of God;
5Having a form of godliness, but denying the power thereof: from such turn away.
2 Timothy 3:1-4
Judas fooled everyone EXCEPT the one who mattered.
1 Corinthians 5:11
11 But now I have written unto you not to keep company, if any man that is called a brother be a fornicator, or covetous, or an idolator, or a railer, or a drunkard, or an extortioner; with such an one no not to eat.
1 Corinthians 15:33
33 Be not deceived: evil communications corrupt good manners.
Just because they LOOK like a Christian , ACT like a Christian and TALK like a Christian.......