I'm so sorry that you have an intolerant christian "Dad." This is a little heartbreaking, and really disheartening. I feel for you and yeah big - big Hug. The semi formal tone of the letter makes me think that it's been re-edited by a few people. Clearly he's been put up to it with the odd bible passage added to it. That last few lines is some one trying to make an emotional tie to the long gone past where he was in charge, and could make all the decisions and you had to obey with out question.
He has done what all customer service people try to do when confronted with conflict. Reframe the issue, and broken record what can be done with the client. Only cold heartless barstards of large corporations and church's do this sort of shit.
The quote "I will not compromise my belief that it is wrong and I refuse to be a participant in it." Is pretty much his starting negotiation position and it looks like he's not budging. The criticizing, the emotional blackmail, the it's your fault bla bla is tired illogical faith based stubbornness.
It's a crazy making place. You are legitimate to feel angry and the "emotional pull of being a child" is as low a blow as you can get. What a stubborn man. I do feel so sorry for him, and I suspect as do you. But we can't get past this crazy church blockade here.
What to do? Well first and foremost you have to protect your self. You cannot be his compliant little daughter anymore, that small child is one part of you - but this braver adult is now you. He can't pick and choose what part of your personality he likes. So he can't call him self "Dad" or make references to your childhood. He has to accept that this is what you are now.
He's also not allowed to meet your girlfriend until he accepts you and your girlfriend all the way through. If you haven't all ready shown her what your dealing with I suggest this could be a good start.
Finally a simple request is the best. Have a talk with him and just see him for what he is. Can he accept that you have grown up? Can be adult enough to have a cup of coffee with you? Is he able to talk freely with out other people prompting him? Only you can judge that. Try talking about other things first. Like light subjects - fun things. Don't let an argument about religion chew up all your time.
The reply?
Dad- Do you want to meet just you and me for a cup of coffee? I'm at this [location] at this [time] I'm not asking for anything, it's just you and me no one else.
Your Daughter.
Oh and Dan Savage also talks about inviting a Christian bigot to dinner in his book American Savage - it's a very good chapter to read.
Good Luck with this I hope this helps.