Supreme Court Justice Antonin Scalia said:

Church and state would not be such a difficult subject if religion were, as the Court apparently thinks it to be, some purely personal avocation that can be indulged entirely in secret, like pornography, in the privacy of one's room.

For most believers it is not that, and has never been. Religious men and women of almost all denominations have felt it necessary to acknowledge and beseech the blessing of God as a people, and not just as individuals, because they believe in the "protection of divine Providence," as the Declaration of Independence put it, not just for individuals but for societies.