Enos could feel the weight of sin lifted from him. This was not an ephemeral experience, but one with tremendous power. The removal of sin was so dramatic as to be conclusive. Enos did not wonder if perhaps he had been forgiven. Enos could feel that the burden of sin was gone, a change in state so dramatic that he inquired of the Lord how it could have happened.
The answer is that the atonement comes through the Savior. This is the crowning message of Nephi and Jacob, and now Enos has his foundational prophetic experience grounded in that very knowledge. Enos will also be a prophet who declares the Christ for he has had personal experience with the saving mission of the coming Messiah.