Jesus told Peter, “People who have washed are completely clean. They need to have only their feet washed. All of you, except for one, are clean.” (Jesus knew who was going to betray him. That's why He said, “All of you, except for one, are clean.”) John 13:10-11 (GW)

Read:  John Chapter 13

I know whom I have chosen, but that the scripture may be fulfilled, he that ate bread with me has lifted up his heel against me. Now I tell you before it come, that, when it is come to pass, ye may believe that I am he. Verily, verily, I say unto you, he that receive whomsoever I send receives me; and he that receives me receives Him that sent me. When Jesus had thus said, He was troubled in spirit, and testified, and said, verily, verily, I say unto you, that one of you shall betray me. John 13:18-21 (KJV)

What is recorded in Psalm 41:9? 

Yea, mine own familiar friend, in whom I trusted, which did eat of my bread, hath lifted up his heel against me.

Who was the Apostate?

Apostasy (/əˈpɒstəsi/; Greek: ἀποστασία (apostasia), 'a defection or revolt', from ἀπό, apo, 'away, apart', στάσις, stasis, 'stand, 'standing') is the formal disaffiliation from or abandonment or renunciation of a religion by a person. One who commits apostasy is known as an apostate.

Consider the Galatian church:

Read Apostle Paul’s letter to the Galatian congregation

I marvel that ye are so soon removed from Him that called you into the grace of Christ unto another gospel, which is not another, but there be some that trouble you, and would pervert the gospel of Christ. Though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed. As we said before, so say I now again, if any man preach any other gospel unto you than that ye have received, let him be accursed.   Do I now persuade men, or GOD, or do I seek to please men?

If I yet pleased men, I should not be the servant of Christ, but I certify you, brethren, that the gospel which was preached of me is not after man. I neither received it of man, neither was I taught it, but by the revelation of Jesus Christ. Ye have heard of my conversation in time past in the Jews' religion, how that beyond measure I persecuted the church of GOD, and wasted it, and profited in the Jews' religion above many my equals in mine own nation, being more exceedingly zealous of the traditions of my fathers; when it pleased GOD, who separated me from my mother's womb, and called me by His grace, to reveal His Son in me, that I might preach Him among the heathen; immediately I conferred not with flesh and blood. Galatians 1:6-16 (KJV)

O foolish Galatians, who hath bewitched you, that ye should not obey the truth, before whose eyes Jesus Christ hath been evidently set forth, crucified among you?  This only would I learn of you, received ye the Spirit by the works of the law, or by the hearing of faith? Are ye so foolish having begun in the Spirit, are ye now made perfect by the flesh? Have ye suffered so many things in vain, if it be yet in vain? He therefore that ministers to you the Spirit, and works miracles among you, does He it by the works of the law, or by the hearing of faith?

Justification is by FAITH

Even as Abraham believed GOD, and it was accounted to him for righteousness. Know ye therefore that they which are of faith, the same are the children of Abraham. And the scripture, foreseeing that GOD would justify the heathen through faith, preached before the gospel unto Abraham, saying, in thee shall all nations be blessed. So then they which be of faith are blessed with faithful Abraham. For as many as are of the works of the law are under the curse: for it is written, cursed is every one that continues not in all things which are written in the book of the law to do them. No man is justified by the law in the sight of GOD, it is evident, for, the just shall live by faith. The law is not of faith, but, the man that does them shall live in them. Christ hath redeemed us from the curse of the law, being made a curse for us, for it is written, cursed is every one that hangs on a tree; that the blessing of Abraham might come on the Gentiles through Jesus Christ; that we might receive the promise of the Spirit through faith.

 Brethren, I speak after the manner of men, though it be but a man's covenant, yet if it be confirmed, no man disannulled, or added thereto. Now to Abraham and his seed were the promises made. He said not, and to seeds, as of many; but as of one, and to thy seed, which is Christ. This I say, that the covenant, that was confirmed before of GOD in Christ, the law, which was four hundred and thirty years after, cannot disannul, that it should make the promise of none effect.  If the inheritance be of the law, it is no more of promise, but God gave it to Abraham by promise.

Wherefore then serve the law?

It was added because of transgressions, till the Seed should come to whom the promise was made; and it was ordained by angels in the hand of a mediator. Now a mediator is not a mediator of one, but GOD is one.  Is the law then against the promises of GOD, GOD forbid, for if there had been a law given which could have given life, verily righteousness should have been by the law, but the scripture hath concluded all under sin, that the promise by faith of Jesus Christ might be given to them that believe.

Before faith came, we were kept under the law, shut up unto the faith which should afterwards be revealed. Wherefore the law was our schoolmaster to bring us unto Christ, that we might be justified by faith. After that faith is come, we are no longer under a schoolmaster, for ye are all the children of GOD by faith in Christ Jesus. As many of you as have been baptized into Christ have put on Christ. There is neither Jew nor Greek, there is neither bond nor free, there is neither male nor female, for ye are all one in Christ Jesus, and if ye be Christ's, then are ye Abraham's seed, and heirs according to the promise. Galatians 3:1-29 (KJV)

Evil Heart of Unbelief

Take heed, brethren, lest there be in any of you an evil heart of unbelief, in departing from the living GOD. Exhort one another daily, while it is called today; lest any of you be hardened through the deceitfulness of sin. We are made partakers of Christ, if we hold the beginning of our confidence steadfast unto the end; While it is said, today if ye will hear His voice, harden not your hearts, as in the provocation, for some, when they had heard, did provoke; howbeit not all that came out of Egypt by Moses. With who was He grieved forty years? Was it not with them that had sinned, whose carcasses fell in the wilderness? And to whom swore He that they should not enter into His rest, but to them that believed not? So we see that they could not enter in because of unbelief.

Hebrew 3:12-19 (KJV)

The Day of Salvation

We then, as workers together with Him, beseech you also that ye receive not the Grace of GOD in vain. (He saith, I have heard thee in a time accepted, and in the day of salvation have I succored thee; behold, now is the accepted time; behold, now is the day of salvation.) II Corinthians 6:1-2 (KJV)