I am very sorry for saying ___________. I understand it was hurtful. Will you please forgive me?

You are apparently looking for a way to write to this person, as opposed to a face-to-face meeting. I think you should use the word 'apology' and make a reference to your mistake, but don't actually repeat the word or words that you now regret. For example: >> "Dear Robert, I really want to apologize for the things I said to you last week after class. ... " ... or, if there weren't 'things', but rather just a word, or a few words ... >> "Dear Robert, I really want to apologize for what I said to you last week after class. ... " You can go on to say ... >> "I know that my words were unkind and hurtful, and I truly regret my behavior." >> "Speaking out harshly, without regard for the feelings of others, is not acceptable. It is not the kind of person I want to be." If you believe the relationship can be repaired, you might say ... >> "I hope you can find it within yourself to forgive me, and that you will allow me the opportunity to regain your trust and friendship in the future." I DO NOT think that you should ramble on with long explanations, and in particular, do not (as suggested by an earlier answer) bring "god" into the discussion. Keep this between you and your acquaintance, and leave out any talk of 'devine' inspiration. Why? Because what you are saying here is that there really is no good excuse for your ill-chosen words, no matter the circumstances. So you keep it 'short and sweet' -- make the apology, hold out the hope for a renewed relationship in the future, and then close with ... >> "Sincerely, Stella" ... or ... >> "Very sincerely, Stella" I might add that regardless of how this person receives your apology, you can have the peace of mind knowing that, in the end, you did the right thing. If this person chooses not to accept your apology, you have no control over that. In your own heart, you will know that it was sincere, and that is the most important thing.