To hear a sorry from a Christian when you are not a believer yourself, or not the kind of believer who does apologize, is not only humbling for the person saying sorry. I overheard a woman apologize to another woman about a conflict they had. After hearing it, I wondered, “Would I ever have the guts to do something like that?” I think it also might humble the person you are apologizing to, because they may wonder what it is about you that would be apologetic and sincere. Don’t think so much about if it’s sinful or not sinful not to. I think it would be better to look at the impact those two little words could have on your self, the person you say those words to, or anyone who might overhear or be told about it later.