Most of Christianity has it only partially right. It is true: It is man's nature to sin! "If we say that we have no sin, we deceive ourselves, and the truth is not in us. If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness. If we say we have not sinned, we make him a liar, and his word is not in us." I John 1:8-10
Sin is the disobedience of God's Law and commandments. "Whosoever committeth sin transgresseth also the law: for sin is the transgression of the law. And ye know that he was manifested to take away our sins; and in him is no sin. Whosoever abideth in him sinneth not: whosoever sinneth hath not seen him, neither known him.
"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.
"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. 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." I John 3:4-10
There you have it! If one who claims to be a Christian is still partaking of sin, the Bible says, he is of the devil. To be a Christian, one must overcome the temptation to commit sin. The only way one can overcome sin is to receive the indwelling Spirit of God, which is the Holy Ghost. This is the power to become a son of God. (see John 1:12-13) One must receive the Holy Ghost and be led by the Spirit of God to overcome sin. "For as many as are led by the Spirit of God, they are the sons of God."
Therefore, if you find yourself still committing sin, you are not yet "born again", no matter how much you declare it to be so.
Throughout the Bible, God condemns sin. All the examples in the Bible have been documented to show that sin is worthy of God's anger. Adam and Eve were the first examples of God's judgement against those that were disobedient to God's commandments. God made Adam and Eve an example, that every man would be held accountable for his sin.
"And Moses said unto the people, Fear not: for God is come to prove you, and that his fear may be before your faces, that ye sin not." Exodus 20:20
Jesus said, "Verily, verily, I say unto you, whosoever committeth sin is the servant of sin." John 8:34 Jesus came to give us an example of how to overcome sin.
"For even hereunto were ye called: because Christ also suffered for us, leaving us an example, that ye should follow his steps: who did no sin, neither was guile found in his mouth: who, when he was reviled, reviled not again; when he suffered, he threatened not; but committed himself to him that judgeth righteously:" I Peter 1:21-23
"Then Jesus said unto his disciples, If any man will come after me, let him deny himself, and take up his cross (exposure to death), and follow me." Matthew 16:24
The only way to be a Christian (Christ-like) is to follow the example Jesus Christ left for us. If we deny ourselves and follow him, we will not sin. This is how he came to destroy the works of the devil. The works of the devil is sin.
"Therefore, brethren, we are debtors, not to the flesh, to live after the flesh. For if ye live after the flesh, ye shall die: but if ye through the Spirit do mortify the deeds of the body, ye shall live." Romans 8:12-13
"Knowing this, that our old man is crucified with him, that the body of sin might be destroyed, that henceforth we should not serve sin." Romans 6:6
"If ye then be risen with Christ, seek those things which are above, where Christ sitteth on the right hand of God. Set your affections on things above, not on things on the earth. For ye are dead, and your life is hid with Christ in God. When Christ, who is our life, shall appear, then shall ye also appear with him in glory.
"Mortify therefore your members which are upon the earth; fornication, uncleanness, inordinate affection, evil concupiscence, and covetousness, which is idolatry: for which things sake the wrath of God cometh on the children of disobedience: In the which ye also walked some time, when ye lived in them.
"But now ye also put off all these; anger, wrath, malice, blasphemy, filthy communication out of your mouth. Lie not one to another, seeing that ye have put off the old man with his deeds; and have put on the new man, which is renewed in knowledge after the image of him that created him: Colossians 3:1-10
"For the wages of sin is death; but the gift of God is eternal life through Jesus Christ our Lord (his example)." Romans 6:23