Seventy times seven — and why the number is the point.
Forgiveness is the teaching people quote most and practise least, usually because it has been flattened into "let it go". That is not what he said, and the difference matters a great deal when the thing you are being asked to forgive was serious.
Here is the shape of his teaching on it, and one exchange opened properly.
I don't tell you until seven times, but, until seventy times seven.
Peter had asked whether seven times was enough, and he was being generous — the rabbinic guidance of the time suggested three. Jesus does not answer with a larger allowance. Four hundred and ninety is not a ceiling; it is a joke about ceilings, and the joke is that Peter was still counting.
In his teaching, forgiveness is never described as a feeling that arrives, and never as pretending the thing did not happen. It is closer to a decision about what you are going to keep carrying — which is why he can command it at all, since nobody can be commanded to feel differently.
It is also, almost everywhere he raises it, tied to having been forgiven yourself. The unforgiving servant is not punished for a lack of warmth. He is punished for taking something he would not give.
Walking with Jesus: Devotional has a collection called Jesus on Forgiveness that walks these teachings one a day — each with the passage around it, a short reflection, a prayer and one thing to carry into the day.
It is a one-time purchase, about five minutes a morning, and it never asks you to catch up.