There have been several threads on this in the past:
https://www.swingersboard.com/forums/topic/57341-religion-and-swinging/
https://www.swingersboard.com/forums/topic/40150-christian-swingers/
https://www.swingersboard.com/forums/topic/54819-the-bible-interpreting-it-and-swinging/
There are several more but these are ones that I recall from fairly recent times. Heck, if you do any research about the 'lost books of the Bible' you will find out that there are dozens of books that have been included and excluded from the Bible over time. One other site that I have kept bookmarked is this:
Monogamy Isn't Biblical, It's Roman
I always wondered why the Old Testament had men marrying multiple wives and then it just stopped in the New Testament. This explains a lot of the why.
Bottom line is we both believe in God and are religious, but we also believe that whatever anyone else believes in, as long as it makes them a better person and doesn't hurt others, is a good thing and should be allowed and encouraged. I would hate to be in front of the gates of heaven only to see Buddha or Allah or The Great Spirit was the 'right' God and have Him tell us 'you picked the wrong God...sorry, you are out'. I believe that this won't happen, but at the same time believe that God wouldn't be so religious exclusive (only one 'right' religion and everyone else goes to Hell). Most organized religion teaches 'be a good person and be nice to everyone else'...we do our best to adhere to this although we identify ourselves as Christian. Swinging is something that we do TOGETHER in the light, not behind the back of our SO in the dark. It doesn't 'hurt' either one of us and we do our best not to allow it to hurt anyone else. We don't see where it goes against our 'makes them a better person and doesn't hurt others' belief so we don't have a conflict or issue with the two. We try, as instructed by the Bible, not to judge others and keep our stone casting in check.
Sorry, but I was brought up in a strict religious household and I have spent a great deal of time wrestling with this subject. I'll just shut up now...for a few minutes at least.