The forgiveness of sins;

This is the great hope Christians have. Not eternal life; everyone gets that, but most people have to spend it in Hell.

We all need forgiveness,  because we've already sinned ourselves to death. Sin is just going against God. He won't put up with sin now, what makes you think he'll put up with it for eternity in Heaven?

The reason -- the only reason -- we can be accepted by the Father is to that our sins are forgiven, and the only way that could happen is that the Son had to die to pay for them.