How long will God continue to forgive?

But now thus saith the Lord that created thee, O Jacob, and he that formed thee, O Israel, Fear not: for I have redeemed thee, I have called thee by thy name; thou art mine.

25 I, even I, am he that blotteth out thy transgressions for mine own sake, and will not remember thy sins.

21 Remember these, O Jacob and Israel; for thou art my servant: I have formed thee; thou art my servant: O Israel, thou shalt not be forgotten of me.

22 I have blotted out, as a thick cloud, thy transgressions, and, as a cloud, thy sins: return unto me; for I have redeemed thee.

So many woes prophesied throughout Isaiah because of continual transgression, but how gracious is God who entreats, redeems, who blots out our transgressions - the key is returning to Him.

You ask how long will God continue to forgive. There must be a cut of point . is it 1 Thessalonians 4:16?