The time in which the Founding Fathers established what would become the United States was a time period of religious persecution in many parts of the world. This was one of the main concerns of the Founding Fathers, leading to the establishment of freedom of religion. Many of the Founding Fathers were devout Christians, and wanted to establish a land where Christians were able to actively practice without being persecuted.
The Founding Fathers were after freedom from tyranny, and while some of this was religious, it was not their primary focus. They were religious men, and no doubt their beliefs were important to them and formed many of their decisions, but it was not with religion in mind that they wrote the constitution.
Despite the original colonies being essentially religiously founded, the vision of the founding fathers was a secular nation where such issues could not become divisive in government. There isn't much to read into beyond the actual division of church and state drafted in our Constitution, which was included although a number of the founding fathers were deists of one stripe or another in religious orientation.
The founding of the United States was revolutionary in many respects, one of which was that it was founded without a state church or religion. This was extraordinary for the time period and not a coincidence. Many of the Founding Fathers were skeptical or critical of religion. Benjamin Franklin and Thomas Jefferson's objections are well documented for example.