Early warnings of grave misunderstandings of Christianity

Among the riskiest hypotheses about the message of the Christian Bible are surely those hypotheses, "teachings", or "doctrines" that describe how God judges Christians. If anyone proposes a theory that Christians can act immorally without consequences from God's hand, when consequences do exist, the potential destructiveness seems almost limitless: great injury to the person duped into acting immorally, to those persons he or she acts immorally against, and to the person who led the fraud. 
      This form of misunderstanding of Christianity - moral libertarianism, antinomianism, or lawlessness - appears to have arisen so fast that several or even all of the apostles and books of the New Testament strive to point out the misunderstanding and correct it. To begin with, the Lord, Christ Jesus, warned beforehand of it in the Sermon on the Mount:

"Beware of false prophets, which come to you in sheep’s clothing, but inwardly they are ravening wolves. Ye shall know them by their fruits. Do men gather grapes of thorns, or figs of thistles? Even so every good tree bringeth forth good fruit; but a corrupt tree bringeth forth evil fruit. A good tree cannot bring forth evil fruit, neither can a corrupt tree bring forth good fruit. Every tree that bringeth not forth good fruit is hewn down, and cast into the fire. Wherefore by their fruits ye shall know them. Not 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. Many 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? And then will I profess unto them, I never knew you: depart from me, ye that work iniquity." (Matthew 7:15-23, AKJV)

After the Lord we might listen first to the apostle St. John:

"Little children, let no man deceive you: he that doeth righteousness is righteous, even as he is righteous. 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." (1 John 3:7-8, AKJV) 

Then Paul:

"Know ye not that the unrighteous shall not inherit the kingdom of God? Be not deceived: neither fornicators, nor idolaters, nor adulterers, nor cowardly, nor abusers of themselves with mankind, nor thieves, nor covetous, nor drunkards, nor revilers, nor extortioners, shall inherit the kingdom of God." (1 Corinthians 6:9-10,)

And Peter:

"Wherefore gird up the loins of your mind, be sober, and hope to the end for the grace that is to be brought unto you at the revelation of Jesus Christ; as obedient children, not fashioning yourselves according to the former lusts in your ignorance: but as he which hath called you is holy, so be ye holy in all manner of conversation; because it is written, Be ye holy; for I am holy. And if ye call on the Father, who without respect of persons judgeth according to every man’s work, pass the time of your sojourning here in fear...." (1 Peter 1:13-17, AKJV)

AKJV: Scripture quotations from The Authorized (King James) Version. Rights in the Authorized Version in the United Kingdom are vested in the Crown. Reproduced by permission of the Crown’s patentee, Cambridge University Press.