Ephesians 4:32
And be ye kind one to another, tenderhearted, forgiving one another, even as God for Christ's sake hath forgiven you.
I agree with the verse, I dont believe he is showing finality in that picture but a lesson there because of that TILL, I cant see how it is final with a TILL in there.
And beause as much as we are forgiven of Him as sinners, we also need to learn of Him, and we dont always do this perfectly, and there are times of doing wrongly (ie not extending mercy as we should) holding a grudge (as I have been guilty of) and he is showing us the game plan if we do not and what our heavenly Father will do to us. Theres a TILL
Otherwise, if you have not shewed mercy (even once) has sealed your fate for ever, whereas Paul encourages them to be forgiving, tender hearted, reminds them that love keeps no records of wrongs etc, thats the aim, our desire to be accepted of Him and doing those things that please him. Does it look like they did so always? No, but thats what being chastised is about too. To learn to do right as he teaches sinners in the way.