Q. Should a Sinner Leave the Church?
The first question you have raised in my mind is whether you are now a Christian or not. Christians sometimes sin, but you seem to assume that your persistent and willful sin is evidence that you never really trusted in Christ for salvation. And you may be right. Trying harder to live a good life is not the way to obtain God’s salvation. We can never earn our salvation by good works:
8 For by grace you have been saved through faith; and that not of yourselves, it is the gift of God; 9 not as a result of works, so that no one may boast. 10 For we are His workmanship, created in Christ Jesus for good works, which God prepared beforehand so that we would walk in them (Ephesians 2:8-10, NASB).
4 But when the kindness of God our Savior and His love for mankind appeared, 5 He saved us, not on the basis of deeds which we have done in righteousness, but according to His mercy, by the washing of regeneration and renewing by the Holy Spirit, 6 whom He poured out upon us richly through Jesus Christ our Savior, 7 so that being justified by His grace we would be made heirs according to the hope of eternal life. 8 This is a trustworthy statement; and concerning these things I want you to speak confidently, so that those who have believed God will be careful to engage in good deeds. These things are good and profitable for men. Titus 3:4-8 (NASB)
As Paul says to the Ephesians, and to Titus above, good works cannot save us, but they are the fruit which salvation produces. Don’t try to earn enough favor from God by working hard at being good, because it won’t work.
Salvation is the result of the goodness of Jesus Christ. He lived a perfect life and then died on the cross of Calvary to bear the punishment for our sins, and to give us new life. That is what Paul is telling us in the verses below:
1 What shall we say then? Are we to continue in sin so that grace may increase? 2 May it never be! How shall we who died to sin still live in it? 3 Or do you not know that all of us who have been baptized into Christ Jesus have been baptized into His death? 4 Therefore we have been buried with Him through baptism into death, so that as Christ was raised from the dead through the glory of the Father, so we too might walk in newness of life. 5 For if we have become united with Him in the likeness of His death, certainly we shall also be in the likeness of His resurrection, 6 knowing this, that our old self was crucified with Him, in order that our body of sin might be done away with, so that we would no longer be slaves to sin; 7 for he who has died is freed from sin. 8 Now if we have died with Christ, we believe that we shall also live with Him, 9 knowing that Christ, having been raised from the dead, is never to die again; death no longer is master over Him. 10 For the death that He died, He died to sin once for all; but the life that He lives, He lives to God. 11 Even so consider yourselves to be dead to sin, but alive to God in Christ Jesus. 12 Therefore do not let sin reign in your mortal body so that you obey its lusts, 13 and do not go on presenting the members of your body to sin as instruments of unrighteousness; but present yourselves to God as those alive from the dead, and your members as instruments of righteousness to God (Romans 6:1-13).
If you are telling me that you have now trusted Christ and that your desire is to forsake your sin and to walk in fellowship with God then it is vitally important for you to establish and maintain fellowship with a good, Bible teaching church.
We know from Matthew 18:15-20 and 1 Corinthians chapter 5 that it is sometimes necessary for the church to discipline a professing Christian who refuses to accept correction and to flee from sin. That is something the church does, although sometimes the sinner will leave the church because he or she is uncomfortable with God's people.
22 let us draw near with a sincere heart in full assurance of faith, having our hearts sprinkled clean from an evil conscience and our bodies washed with pure water. 23 Let us hold fast the confession of our hope without wavering, for He who promised is faithful; 24 and let us consider how to stimulate one another to love and good deeds, 25 not forsaking our own assembling together, as is the habit of some, but encouraging one another; and all the more as you see the day drawing near (Hebrews 10:22-25).
Church is where you receive teaching, encouragement, and correction. It is where others can minister to your needs and you can minister to others (Ephesians 4:1-16). I would encourage you to confess your sins to the church (or at least to one of the church leaders) and express your desire to walk in fellowship with our Lord and with His people. Ask your fellow believers to uphold you in prayer.
Forsaking God's Word, God's people, and worship is never a sign of spiritual health, and it is a very dangerous thing to do.