There is a difference between solved and forgiven. People, including Christians sin, but the latter do not do so intentionally. We are forgiven, unlike those who continually sin intentionally.As @Trailblazer also pointed out. What sins have been solved? people still do things that are clearly against the law of God, which is considered to be a sin according to the bible.
Do you mean that God doesn't care about it anymore or won't punish for it, or how is it supposed to be understood?
The punishment for sin has been paid for by Christ's sacrifice.
Try thinking about what I have written. You may gain understanding.