Peter, Paul, James and Johnall warned the New Covenant Church that what they were doing and not doing would reveal the truth of their claim to faith. Paul warned people to test their faith to make sure they were not deceived.
Even John warns that we need to walk according to what Jesus showed us and confess our sins if we are to be cleansed of unrighteousness. John even gives the keeping of the commandments as the rod by which we measure the truth of our faith. And those who do not keep the commandments are a liar and Christ is not in them. Over and over John repeats that he that "doeth not righteousness" is not born again of Christ and the Father. And John warns us that we may not only be deceived but may deceive ourselves  warning us of the many false teachers who are "out in the world".
The Bible from the beginning warns and continues those warnings throughout the New Testament that many will be decieved thinking they are believers while in truth they are workers of iniquity. Because these warnings are ignored by the modern Church, the welfare of a foolish society has become a snare.
- “It is impossible to introduce into society a greater change and a greater evil than this: the conversion of the law into an instrument of plunder.”
- 2 Peter 2:14 "Having eyes full of adultery, and that cannot cease from sin; beguiling unstable souls: an heart they have exercised with covetous practices; curse children:"
- 2 Peter 2:3 "And through covetousness shall they with feigned words make merchandise of you: whose judgment now of a long time lingereth not, and their damnation slumbereth not."
- Ephesians 5:1 ¶ Be ye therefore followers of God, as dear children; 2 And walk in love, as Christ also hath loved us, and hath given himself for us an offering and a sacrifice to God for a sweetsmelling savour. 3 ¶ But fornication, and all uncleanness, or covetousness, let it not be once named among you, as becometh saints; 4 Neither filthiness, nor foolish talking, nor jesting, which are not convenient: but rather giving of thanks. 5 For this ye know, that no whoremonger, nor unclean person, nor covetous man, who is an idolater, hath any inheritance in the kingdom of Christ and of God. 6 Let no man deceive you with vain words: for because of these things cometh the wrath of God upon the children of disobedience. 7 Be not ye therefore partakers with them. 8 For ye were sometimes darkness, but now are ye light in the Lord: walk as children of light: 9 (For the fruit of the Spirit is in all goodness and righteousness and truth;) 10 Proving what is acceptable unto the Lord. 11 And have no fellowship with the unfruitful works of darkness, but rather reprove them.
- "Stand fast therefore in the liberty wherewith Christ hath made us free, and be not entangled again with the yoke of bondage." Galatians 5:1 Galatians 5:15 "But if ye bite and devour one another, take heed that ye be not consumed one of another."
- 1 Corinthians 6:9 "Know ye not that the unrighteous shall not inherit the kingdom of God? Be not deceived: neither fornicators, nor idolaters, nor adulterers, nor effeminate, nor abusers of themselves with mankind, 10 Nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners, shall inherit the kingdom of God.
- James 5:12 ¶ But above all things, my brethren, swear not, neither by heaven, neither by the earth, neither by any other oath: but let your yea be yea; and [your] nay, nay; lest ye fall into condemnation.
- 1 John 2:6 He that saith he abideth in him ought himself also so to walk, even as he walked.
- 1 John 2:11 But he that hateth his brother is in darkness, and walketh in darkness, and knoweth not whither he goeth, because that darkness hath blinded his eyes.
- 2 John 1:4 I rejoiced greatly that I found of thy children walking in truth, as we have received a commandment from the Father.
- 2 John 1:6 And this is love, that we walk after his commandments. This is the commandment, That, as ye have heard from the beginning, ye should walk in it.
- 3 John 1:3 For I rejoiced greatly, when the brethren came and testified of the truth that is in thee, even as thou walkest in the truth. 4 I have no greater joy than to hear that my children walk in truth... 11 Beloved, follow not that which is evil, but that which is good. He that doeth good is of God: but he that doeth evil hath not seen God.
- 1 John 3:7 Little children, let no man deceive you: he that doeth righteousness is righteous, even as he is righteous. 8 He that committeth sin is of the devil; for the devil sinneth from the beginning. For this purpose the Son of God was manifested, that he might destroy the works of the devil. 9 Whosoever is born of God doth not commit sin; for his seed remaineth in him: and he cannot sin, because he is born of God. 10 In this the children of God are manifest, and the children of the devil: whosoever doeth not righteousness is not of God, neither he that loveth not his brother.
- 1 John 3:24 And he that keepeth his commandments dwelleth in him, and he in him. And hereby we know that he abideth in us, by the Spirit which he hath given us.