Did you know that the Bible speaks of two kinds of sin? One we inherit from Adam, which is the propensity to do wrong even against our better judgment. Paul spoke of this...
"I find, then, this law in my case: When I wish to do what is right, what is bad is present with me. 22 I really delight in the law of God according to the man I am within, 23 but I see in my body another law warring against the law of my mind and leading me captive to sin’s law that is in my body. 24 Miserable man that I am! Who will rescue me from the body undergoing this death? 25 Thanks to God through Jesus Christ our Lord! So, then, with my mind I myself am a slave to God’s law, but with my flesh to sin’s law." (Romans 7:21-25)
These momentary lapses are common to all of us.....and this is the sin Jesus came to forgive and to eradicate from humanity forever.
The other kind of sin is the one we practice willfully.....we already know that it is wrong, but it is not just a lapse in judgment...it is a conscious decision to commit a serious wrong. Like the devil did in the garden of Eden. He deliberately planned his moves knowing that it would cause death to mankind. Adam was faced with a similar decision...to obey his God, or to join his wife in rebellion.....he deliberately chose to join his wife. The consequences were dire. Both were perfect and without the defect of sin until they had carried out the action.....(Rom 5:12) These are the sins that cannot be forgiven without sincere repentance......Manasseh proved that. He was doing what God detested and yet when the chips were down, he genuinely repented and followed through with his actions.....sinning that way no more. It is all God asks of us.