I am very glad that the founders recognized that God is immutable, i.e. they used the word unalienable.
After all, if God could change, our rights would not be unalienable and thus, negotiable. If the rights were granted by human device, they could be withdrawn in the same fashion. Indeed, we are only secure in our rights, when the majority believes in the immutable Creator.
I think that term was used in connection with rights, not God. It's a legal term, meaning "cannot be sold or given away." In other words, you can't sell your life, liberty, or your right to own property. Such rights are inherent in you, and stay with you as long as you live. "Alienability" was a hot concept back then, because in the feudal system, land wasn't alienable -- it stayed with the owner and his progeny.