Our Founders were serious about keeping government completely out of the business of expounding religious doctrine.
In their time, there were no state-sanctioned inscriptions, mottos, currencies or oaths which mentioned God at all. The one national motto, E Pluribus Unum, was in secular Latin, and meant “Out Of Many, One.”
Then, as now, individual politicians expressed their views of divinity in public utterances -- individual religious expression was and remains protected by the Free Exercise clause. But official government dicta on God was considered an establishment of religion by the state and strictly prohibited by the Constitution.
Ours was the first entirely secular government created on the face of the planet, and one of the greatest human accomplishments of all time.
All of it done to protect the wide variety of religious belief deeply held by individual American citizens.