Hebrews 9:26, But He has appeared, once for all, at the end of the ages to put away sin by the sacrifice of himself.

2 Corinthians 5:19, In Christ God was reconciling the world to himself, not counting (our) trespasses against (us).

Such knowledge and trust make a joyful heart, which can surely and truthfully say, “I know of no sin, for they are laid on Christ.  Now, they cannot lie at the same time on Him and on us.  Therefore, no man can say that he has atoned for sin by his own righteousness.  To expiate and abolish sin belongs to Christ alone.

If you believe it, your sins are forgiven, you are holy and righteous and you receive the Holy Spirit, so that from now on you can withstand sin.  And even if in your weakness sin overtake you, it will not be counted against you as long as you remain in faith.  (From a sermon by Martin Luther on the Friday after Easter, 1540)

That is what the forgiveness of sins means.

LSB 543

To god and to the Lamb I will sin, I will sing;

To God and to the Lamb I will sing;

To God and to the Lamb,

Who is the great I AM,

While millions join the theme,

I will sing, I will sing,

While millions join the theme, I will sing.