Believing with you that religion is a matter which lies solely between man & his god, that he owes account to none other for his faith or his worship, that the legitimate powers of government reach actions only and not opinions, I contemplate with sovereign reverence that act of the whole American people which declared that their legislature should "make no law respecting an establishment of religion, or prohibiting the free exercise thereof;" thus building a wall of eternal separation between Church & State.
He probably reflected on the fact that nothing on Earth is truly eternal... and as long as people wish to inflict their religious beliefs on others, and as long as governments have power, then there will be religious people who use the power of government to inflict their beliefs on others. It is the triumph of the U.S. Constitution that it has so far put up a good fight against those never-ceasing and dangerous movements.