What is eternal sin? Jesus was the only one who mentions it in the bible, as well as providing us with the explanation of what it is. Anyone who blasphemes against the Holy Spirit (which is the same as eternal sin) will never be forgiven. Other types of sins can be forgiven including adultery, murder, and even disowning Jesus, but not that form of blasphemy. The ones who actually committed eternal sin accused Jesus of having a demon and believed it was by the power of the devil he cast out demons and performed his miracles (Mark 3:22-30). Only eternal sin cannot be forgiven. Those who have lived in all other types of sin can get saved.
Dan Corner is a holiness preacher who discusses this and many other important issues relevant for Christians on his website. For those who want to be saved but who fear they have committed too many sins, he shows from the Bible how others have found peace with God.