I wrote a good comment a while ago, but the database suspension ate it. Let me try and run down the gist. While Freedom of Religion in the US existed beforehand, the concept of Whiteness wasn't really solidified until after Bacon's Rebellion in the late 1600's. One of the things often overlooked in US history, besides all the slave rebellions, is that the enslaved vastly outnumbered thenon-enslaved throughout most of Colonial America's existence. In order to try and temper that massive danger, the slaveowners tried to import more non-enslaved peoples over in the form of indentured servants and plain old poor people. But this required them pulling from all sort of locations to do so, and if you know your European history, you'll know that just because most of these people believe in Christ, doesn't mean that all these people agreed on how to do it, or coexist peacefully. Freedom of Religion became the way to ensure that all the whites had their choice of religion and that they weren't allowed to attack each other over it, nor was the government supposed to be able to takes sides.

I very much recommend reading the The Counter-Revolution of 1776: Slave Resistance and the Origins of the United States of America by Gerald Horne and checking out this talk by Parenti Real History: Myths of the Founding Fathers, noting however, that all the criticism that Parenti has for the constitution still applies to Bill of Rights. Most of the "Rights" were bribes for the richer americans to get on board with the new Union. That they still benefited the poor was largely a coincidence in much the same way that poor whites in america will fight for tax cuts despite them largely benefiting the rich.

Oh! Another fun fact. The creation of Georgia was as a white's only anti-slavery colony as a means of acting as a firewall between the colonies and St Augustine, where Spain was arming runaway slaves to go back and perform raids on the colonies to put pressure on the Great Britain. :the-more-you-know: