Why is this moral truth?
Life - the way our Founders understood this complete concept actually goes deeply into Mosaic Law and the understanding of the Blessings and Curses inherent within the instruction given to Moses to choose life over death.
Liberty was understood by our Founders to be that inalienable ideal outlined by Mosaic Law and Aristotelean principles. God gives man liberty for man's benefit so that man can freely choose God through his will and intellect.
The pursuit of Happiness is a very deep concept that doesn't mean what most people think it is today. Happiness is the end result of living a virtuous life so that one will be ready to spend the rest of eternity with God.
There are plenty of other moral truths contained within our Founding documents.
Here’s a “Founding Document” than not many are even aware of:
http://unclejaque.wordpress.com/2009/12/28/the-forgotten-declaration-of-1775/
No mention of the Bible.
A satanic cult could come up with its own interpretation of life, liberty and happiness, directly opposed to the message of the Bible.
Aristotle’s writings make no reference of the Bible and vice versa.