ONLY MY OPINION
I have no problem with low necklines showing some cleavage if that's what you are comfortable in, and I'm not a religious fanatic. However I would like to give young brides something to think about.
I am in the position to see a lot of brides every year, and the styles these last few years have been revealingly low cut. I find this to be in poor taste for two reasons.
First, anyone who wears low-cut is asking for attention to that area. Shouldn't your wedding day at least be the one day you need or want attention of that kind only from that one important man? If it's important for you to have everyone stare at your cleavage on the day you wed, that's in poor taste but still acceptable.
Second, however is walking down a church isle with your boobs bouncing out of your gown. That, to me is not only in poor taste, but it's low class and very tacky.
There is an easy solution. I have seen some beautiful floor length lace jackets , that when worn over the wedding gown , actually look like part of the dress, but are easily taken off when you leave the church. Consider what I've said and then do what you feel most comfortable doing. Just my own 2 cents!