The original intention of the Founders was that the land churches were built on belonged to God; we were just stewarding it temporarily. As such, it should not be subjected to the same taxes as the populace...

The First amendment:

Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.

Where does the it say that land on which churches are built belongs to God? The point of the first amendment is to protect religious minorities from government intrusion or persecution by preferentially adopting one religion over another. Taxes have nothing to do with it. There was no such thing as an income tax in the USA until the Civil War, so I'm not sure this is what they had in mind. Which groups do and do not receive tax exemption is a matter of current policy and popular sentiment, not some grand design put forth by the Framers.