Sammies, the constitution is NOT a christian document. One could argue that it is "culturally" christian, but there is absolutely nothing in there about doing unto others and not casting stones or the good samaritan. So those are not actually relevent arguments. (Edit to say: Sammies, I know this wasn't your argument---I just was agreeing with some things you said and then diverged!)
It draws strongly from the Magna Carta, which in turn drew strongly on principals established in ancient Greece---PAGAN ancient Greece. The notion that all men were created equal was first advanced by PAGAN Greek philosopher Epicurus in the 4th century BCE. Thomas Jefferson considered himself a student of Epicurean philosophy and it made it into the Declaration of Independence.
He taught that happiness should be maximized and harm minimized. This led John Locke to argue that all people had a right to pursue life, liberty and property and this was reworked to say Life, Liberty and the Pursuit of Happiness. Since "property" was also considered to be one's own being, happiness was a natural evolution.
It's been a while since I learned this, but I still have my notes. I should pull them out and read them again, but this is what I remember and what I quickly googled to refresh some of it. One thing that really tires me are these claims that the founding fathers were Christians above all else. They were not. It is evidenced in their documents and their concern that the religious would try to impede government. Take a look at DC. PAGANISM EVERYWHERE.
The bible does NOT promote equality. That was a pagan idea carried over by our founding fathers. Check out the Magna Carta. It's a work of art.