That law was thus proposed when it appeared the American Revolution might fail. It was adopted three years before the Constititution was ratified, and six years before 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...") made the Federal protection of religious freedom explicit.
The Brent family initially chose to settle in Maryland, and Margaret Brent was so close to Governor Leonard Calvert (brother of Lord Baltimore) that she served as the executor of his estate. (In the process, she asked for the right to vote, and is often mentioned as the first suffragette and first female lawyer in America.)
However, the political conflicts in Maryland were intense, including several small-scale civil wars, and the Brents moved to Virginia. Margaret Brent was the first English owner of what today is Alexandria. She and her brother Giles was the first English settlers in Northern Virginia.
She built a plantation called "Retirement" while he built "Peace" near Brents Point on Aquia Creek, in what was Northumberland County but is now Stafford County. Giles married Kittamaquad (also spelled as Chitamachen), the daughter of the Piscataway Tayac or chief - just as John Rolfe married Pocahontas, the daughter of Powhatan. Giles Brent's marriage provided him a potential claim to the lands of the tribe, including those of his son Giles Jr.
Brent ended up need the governor and the Governor's Council of Virginia to affirm that his claim to the land on Aquia Creek was based on a grant from the Virginia colonial government. Lord Baltimore tried to claim that *he* was entitled to issue a grant to someone else for the land where Brent had settled,1 because (according to Lord Baltimore...) Potomac Creek marked the Maryland-Virginia boundary.
Giles' nephew, George Brent, later built "Woodstock" on Aquia Creek. He was the only Catholic elected to the colonial Virginia House of Burgesses. The Arlington Diocese of the Catholic Church owns the property of George Brent and has excavated at the site of his colonial home, "Woodstock."2
George Brent married the step-daughter of the third Lord Balimore, maintaining the close ties with the Catholic proprietor across the Potomac River. George Brent had a different relationship with the Native Americans than his uncle Giles, however. In 1675, George Brent led a militia response to the presumed murder of a frontier herdsman by a Doeg Indian. That ended up including a raid across the Potomac River and an attack on settlements in Maryland that resulted in the death of numerous innocent Susquehannock Indians:
In 1686, all was quiet on the northern front. George Brent and three partners obtained a grant from the Crown - one of the last before the Culpeper family took control of their claim to all the land between the Rapahannock and Potomac Rivers, ultimately known as the Fairfax Grant. They also received a special dispensation from James II so settlers on their grant would have freedom to worship in their own manner. Brent and his partners were planning to recruit Huguenots (French Protestants) to the Brent Town tract, south of modern-day Brentsville in what are now Prince William and Fauquier counties. (It was part of Stafford until 1731.) Later, the real estate speculators sought to recruit Catholics to move to their inland parcel, but were unsuccessful.
There's a large crucifix on Route 1 north of Fredericksburg, honoring the Brent family role in establishing "religious liberty" in Virginia. Like so many other Virginia traditions, the facts may not support the claims completely. The Brents deserve acknowledgement as pioneers, and they clearly were Catholic, but the Brent Town project was a real estate venture motivated by a hope of profit and targeted intially towards Protestants, rather than a pioneering initiative to establish religious freedom for Catholics in Virginia.