The United States may pledge a separation of church and state, but that doesn't mean the presidents had no opinions about God. The following quotes from a selection of former presidents offer a glimpse at some of their views.
"No people can be bound to acknowledge and adore the invisible hand which conducts the affairs of men more than the people of the United States. Every step by which they have advanced to the character of an independent nation seems to have been distinguished by some token of providential agency." -- George Washington, First Inaugural Address, April 30, 1789
"Suppose a nation in some distant region should take the Bible for their only law book, and every member should regulate his conduct by the precepts there contained! Every member would be obliged in conscience to temperance, frugality and industry, to justice, kindness and charity towards his fellow men, and to piety, love and reverence toward Almighty God … What a Utopia, what a Paradise would this region be." -- John Adams
"Can the liberties of a nation be secure when we have removed their only firm basis, a conviction in the minds of the people that these liberties are a gift from God?" --Thomas Jefferson, Notes on the State of Virginia, 1785
"Believing with you that religion is a matter which lies solely between man and his God, that he owes account to none other for his faith or his worship, that the legislative 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 separation between church and State." -- Thomas Jefferson in a letter to the Danbury Baptist Association, Jan. 1, 1802
"Before any man can be considered a member of a civil society, he must be considered as a subject of the Governor of the Universe. Religion is the basis and foundation of government." -- James Madison
"A house divided against itself cannot stand." -- Abraham Lincoln's famous words, speaking of the slavery issue in America. He was quoting from Luke 11:17 when accepting the Republican nomination for U.S. Senate from Illinois in June 1858.
"I consider it my greatest joy and glory that, occupying a most exalted position in the nation, I am enabled, simply and sincerely, to preach the practical moralities of the Bible to my fellow countrymen." -- Theodore Roosevelt c. 1906
"America was born a Christian nation. America was born to exemplify that devotion to the elements of righteousness which are derived from the revelations of Holy Scriptures. Ladies and gentlemen, I have a very simple thing to ask of you. I as of every man and woman in this audience that from this night on they will realize that part of the destiny of America lies in their daily perusal of this great book of revelations. That if they would see America free and pure they will make their own spirits free and pure by this baptism of the Holy Scripture." -- Woodrow Wilson at a campaign rally in 1911.
"Our civilization cannot survive materially unless it is redeemed spiritually. It can be saved only by becoming permeated with the spirit of Christ." -- Woodrow Wilson, "The Road Away from Revolution", Atlantic Monthly, August 1923.