Disobedience to God's Word is at the "source" or "origin" of sin, and this is what seperates us from God. When Jesus said, "Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind. This is the first and great commandment. And the second is like unto it, Thou shalt love thy neighbour as thyself. On these two commandments hang all the law and the prophets."(Mt 22:37-40) He was laying out the foundation for a happy and productive life in the love of God via submission to His commandents. It is only when we disobey these founding cornerstones of life that we find ourselves seperated from God by sin.
When Adam and Eve were in the garden, before they disobeyed what God told them, the Bible says, "And they were both naked, the man and his wife, and were not ashamed." (Gen 2:25) It wasn't until after they had disobeyed that the devil convinced them that they should cover up and try to hide their "sin". People have been trying to cover up and hide from God ever since, when all they really have to do is face up to their disobedience to His commandment to love and ask for His forgiveness by the blood of His Son and their spirits are returned to that original innocence before the so-called "fall of man". What did man fall from ? He fell from the grace of God. And how did he do that ? Disobedience !
So, how do we get back to a pure heart in God's eyes ? We must repent (to turn around and go the opposite direction....metanoia in the Greek), change the direction you are on and seek God's forgiveness for sinning against Him and others. How do we accomplish this ? The Bible says,"If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness. " (1Jn 1:9) and that He has specifically made it so that in the name of Jesus, Salvation should be given (Acts 4:12) for it is He who has paid the price of sin for all who come to Him. "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." (1Jn 3:4-5)
"But Jesus said, Suffer little children, and forbid them not, to come unto me: for of such is the kingdom of heaven." (Mt 19:14) For of such child-like innocence is the kingdom of heaven, and you must return to this original innocence in the eyes of God in order to get in. "Except ye be converted, and become as little children, ye shall not enter into the kingdom of heaven." (Mt 18;13) And the only way to achieve this is to be "born again" (converted - Jn 3:3) by cloaking yourself in the blood of Christ, so that the only thing God sees is the righteousness of His Son and no longer your sin of disobedience to Him.
The only sin that is not to be forgiven is what the Bible calls the "blasphemy against the Holy Ghost"." Wherefore I say unto you, All manner of sin and blasphemy shall be forgiven unto men: but the blasphemy against the Holy Ghost shall not be forgiven unto men." (Mt 12:31) What is this "blasphemy" ? To blaspheme the Holy Ghost is to deny that He fathered Jesus and as such makes Christ, God."Of how much sorer punishment, suppose ye, shall he be thought worthy, who hath trodden under foot the Son of God, and hath counted the blood of the covenant, wherewith he was sanctified, an unholy thing, and hath done despite unto the Spirit of grace?" (He 10:29) This is the only thing that will not be forgiven, as it leaves one in the position of still being under the "original sin" of disobedience to God, unforgiven and subject to the punishment laid out in the "law". "For the wages of sin is death; but the gift of God is eternal life through Jesus Christ our Lord." (Ro 6:23)
The end is determined by the present, and the present determines the end. You get to exercise your God-given majesty of choice and apply it to your place in eternity.
"God setteth the solitary in families: he bringeth out those which are bound with chains: but the rebellious dwell in a dry land."(Ps 68:6) The spiritual wilderness is a terrible place to be for a Christian. It's cold and dry when it could be warm and rich in love, in life and in the glorious liberty of the children of God. The choice to obey is yours.