Christians should not sin presumptuously. The Bible tells us plainly to “shun the very appearance of evil. Of course, true believers do not lose their salvation when they sin (read Romans 8:35-39), but even David testified that he had forfeited the joy of salvation (Psalm 51:12). Continuous, deliberate sin will also lead to reprobation. This is a very dangerous position for a believer.

When believers sin, they dishonor Christ (1 Corinthians 6:15-17). They grieve the Holy Spirit (Ephesians 4:30). They also subject themselves to the discipline of a loving Father (Hebrews 12:5-7). If you can continue in sin without experiencing divine discipline, something is terribly wrong. Hebrews 12:8 says: “If you are without discipline, of which all have become partakers, then you are illegitimate children and not sons”.

As for how to deal with a sinning believer, our Lord established a step-by-step process: (I like to refer to it affectionately as “the grievance procedure”)

If your brother sins, go and reprove him in private; if he listens to you, you have won your brother. But if he does not listen to you, take one or two more with you, so that by the mouth of two or three witnesses every fact may be confirmed. And if he refuses to listen to them, tell it to the church; and if he refuses to listen even to the church, let him be to you as a Gentile and a tax-gatherer. Truly I say to you, whatever you shall bind on earth shall be bound in heaven; and whatever you loose on earth shall be loosed in heaven. Again I say to you, that if two of you agree on earth about anything that they may ask, My Father who is in heaven shall do it for them. For where two or three have gathered together in My name, there I am in their midst. (Matthew 18:15-20)

Notice that the discipline process Jesus outlined is specifically intended to determine whether a person in sin is a true brother or an outsider. “If he listens to you (i.e. if he repents), you have won your brother” (v. 15). But ultimately, “if he refuses to listen even to the church, let him be to you as a Gentile and a tax-gatherer” (v. 17)—that is, regard him as an unbeliever and pursue him evangelistically. The Lord goes on to state that He personally mediates His rule on earth through that process (v. 20).

No true believer will persists in willful, deliberate sin and rebellion against the Lord. 5And you know that He was manifested to take away our sins, and in Him there is no sin. 6Whoever abides in Him does not sin. Whoever sins has neither seen Him nor known Him. (1 John 3:5-6)