Letter, George Washington to Samuel Langdon, September 28, 1789: ". . . The man must be bad indeed who can look upon the events of the American Revolution without feeling the warmest gratitude towards the great Author of the Universve whose divine interposition was so frequently manifested in our behalf. And it is my earnest prayer that we may so conduct ourselves as to merit a continuance of those blessings with which we have hitherto been favored. I am etc."James Wilson, "The Laws of Nature," 1790: "Havings thus stated the question--what is the efficient cause of moral obligation? I give it this answer--the will of God. This is the supreme law. His just and full right of imposing laws, and our duty in obeying them, are the sources of our moral obligations. If I am asked: why do you obey the will of God? I answer: because it is my duty to do so. If I am asked again: how do you know this to be your duty? I answer again: because I am told so by my moral sense or conscience. If I am asked a third time: how do you know that you ought to do that, of which your conscience enjoins the performance? I can only say, I feel that such is my duty. Here investigation must stop; reasoning can go no farther. . . ."
Letter from Thomas Jefferson to his friend's son Thomas Jefferson Smith, February 21, 1825: "This letter will, to you, be as one from the dead. The writer will be in the grave before you can weigh its counsels. Your affectionate and excellent father has requested that I would address to you something which might possibly have a favorable influence on the course of life you have to run; and I too, as a namesake, feel an interest in that course. Few words will be necessary, with good dispositions on your part. Adore God, Reverence and cherish your parents. Love your neighbor as yourself, and your country more than yourself. Be just. Be true. Murmur not at the ways of Providence. So shall the life into whic h you have entered, be the portal to one of eternal and ineffable bliss. And if to the dead it is permitted to care for the things of this world, every action of your life will be under my regard. Farewell."
As for people saying or not saying things at different times, for different reasons, even Jesus, who knew His destiny from his youth (and before that, eternity), "fell on His face and prayed, saying, "My Father, if it is possible, let this cup pass from Me. . . ." (Matt. 26:39). He was asking that He would not have to die upon the cross. Yet, just awhile before while at dinner He said: "The Son of Man is to go, just as it is written of Him. . . ." He had been referring to his death for several years, yet prayed in the garden shortly before it was to occur that if were possible, He asks God that it not have to be.
I'll concede that most weren't deists, but a side point is that the most important of them, especially the central drafter Madison and the man with his right ear, Jefferson, were. Others professed Christianity, but did not really practice (actually, I think this is as many today are), or were Unitarian.
Others, of course, were devout Christian of some demonination or another. These people did try to insert a weaker 1st amendment that only required no state-established church, but that was rejected in favor of a more separating version.
I will also concede, to an academic extent, that this nation has some Christian ideals built into it. Given that religion is usually closely tied with societal rules, the Fathers had no choice but to include religious concepts. I will also put forth that the Christian ideal is absolutely not democratic and does not favor the freedom of the individual that this country is based on should it be used as the basis for a political system.
I still hold, however, that despite the individual religious views of the Fathers, all but with a few exceptions saw the mistakes of religious/government entaglement, saw the mistakes of a religious power having secular power, and decided that this country would be founded without any such entanglement in order to preserve the religious and secular freedoms of the people.
The "wall of separation" text was written by Jefferson (yes, I know it's not in the Constitution, as I previously posted) was, believe it or not, in the context of meaning greater religious freedom for religious people -- Baptists in this case. They were being persecuted by the state-sanctioned Congregationalists, and wanted to know if they would continue having the state religion forced upon them. In his letter, Jefferson said, basically, matters of God are personal and that the state should have no say at all in them.