Paul, in his letter to the Christians in Rome had this disheartening statement to make, and it still applies to us:
"Wherefore, as by one man sin entered into the world, and death by sin; and so death passed upon all men, for that all have sinned:" (Romans 5:12 KJV)
There are a number of other statements which give the same accusation upon mankind. When one sins, he is unfit for the kingdom of heaven because there can be no blemishes upon anyone who enters those gates. Under the Old Testament law given to the Israelites, they were to offer sacrifices to God, some times of a lamb others of a bullock, rams, etc., but always without blemish, sometimes said with out spot or blemish. In fact there are 41 separate verses in the Old Testament which specifies one or both of those. These represent those people who are pleasing to God that they be without sin. Sin on a man's soul is a blemish and will make it impossible for him to enter heaven.
So, how then may one ever expect to enter that promised land? The plan was determined before the creation of this universe and man. God, with total omniscience, desired to create man and to give him total free moral agency. And with His ability to know all things, He knew that man would sin. Yet He desired to have him spend eternity with Him. So a plan was designed to offer a man forgiveness of his sins. Since man was weak and totally unable to cleanse himself from sin, there had to be a savior. A sacrifice of a man without spot or blemish to offer to take away man's sins if he would only believe and obey.
You see, once man sins, he no longer has the ability, or right, to rid himself of that sin. He is totally dependent upon the blood of the sinless Son of God to cleanse him of that sin. But there is a way that he can be freed from those sins. But not nearly as easy as many believe and teach. There are numerous people with numerous ideas that all one must do is to repent, or to call upon the name of the Lord, or recite a sinners prayer, or one of many other such things, and he will be home free! Wrong.
The plan which was determined before the creation, fulfilled by Jesus the Son of God, and put into motion on the first Pentecost after Jesus' death burial and resurrection by the apostles, is laid out well in the book of Acts, and the requirements are made clear and are arduous. There are many things which are required of man, none of which cause him to be worthy of the grace of God, but nevertheless, will afford him that grace if pursued with vigor.
Man is incapable of living perfectly as did Jesus. Read here John's explanation.
"This then is the message which we have heard of him, and declare unto you, that God is light, and in him is no darkness at all. If we say that we have fellowship with him, and walk in darkness, we lie, and do not the truth: But if we walk in the light, as he is in the light, we have fellowship one with another, and the blood of Jesus Christ his Son cleanseth us from all sin." (1 John 1:5-7 KJV)
It is strongly recommended that the interested student go and read the entire short first chapter of 1John.
Don't let the terminology cause you to misunderstand what John says here. When he says that God is light an in him is no darkness at all, this simply means God does not sin. The light means his words. If we walk in those words as he does then we have fellowship with him and each other...plus the blood of Jesus Christ continues to cleanse us from all sin. We are incapable of never sinning, but while we are striving to follow his words, any sins we inadvertently commit, will not be charged to us. So, in this sense, we can live totally sin free. Sure we make mistakes but so long as we are trying our best, these sins will not be imputed to us.
"Blessed is the man to whom the Lord will not impute sin." (Romans 4:8 KJV)