God has raised up a horn of salvation for us in the house of his servant David which is speaking of Christ. There is salvation from past sins promised through the grace of God. The grace of God that bringeth salvation hath appeared unto all men teaching us that denying ungodliness and worldy lusts we should live soberly, righteously, and godly in the present world. Since this grace of God appeared to all men we know that this was in the coming of Jesus Christ our savior. His name is Jesus because he saves people from their sins.
Faith is essential to salvation from our past sins.
If thou shalt confess with the mouth the Lord Jesus, and shall believe in thine heart that God hath raised him from the dead, thou shalt be saved. The Gentiles are granted repentance unto life. Confession of faith in Christ is necessary to salvation also. Jesus said that confession of him before men was necessary so he could confess us before the Father in heaven. Open profession of our faith is very necessary to our salvation from past sins.