A letter.
Dear Charles,
My mother was a devout woman. Since her death I've had little use for religion. I've let the holy days pass me by.
Today is Yom Kippur. To specify for a gentile such as yourself, the day of atonement. It's the holiest day. I won't be purposely observing it otherwise, but now that I've known you it would seem too much disrespect to her not to petition for forgiveness when I ought to. I am sorry for causing you to get shot. I don't know that I even believe in forgiveness, but I want you to know that, despite anything else that may occur between us.
I'm writing you this in a letter not because I can't say it to your face, but because our conversations now tend to follow a similar path and I don't want to confuse my intent with anger or my expectations of you. If you find this insufficient, I apologise for that as well.
Erik