"Let him who boasts, boast in the Lord”
Boast anything you want about the Lord. But do not boast that you are "saved". When you boast that your sinning from that point forward will keep you out of hell, you are on the slippery slope to hell, indeed. Woe to him who does not ask the Lord for forgiveness, for he has separated himself from God in the next life, without doubt.
We aren't boasting about sin, we are boasting of His provision of our salvation. Better to boast in Him than deny Him by remaining silent.