The group was protesting outside his concert in Kansas City, Missouri, on Sunday when they filmed the singer taking issue with their stance.
Gill went outside to speak to the church members, and one of them asked: "What in the world are you doing out here?"
He fired back, "I came out to see what hate looks like."
The protester then asked, "What are you doing with another man's wife? Don't you know that divorce plus remarriage equals adultery?"
Grant and Gill were both married to other people before they tied the knot.
Gill responded : "You f---ers are lucky that you don't have a sign that says something about my wife..."
One of the activists then asked Gill his opinion on what Jesus Christ though of adultery, to which the singer said, "He said a lot of stuff about forgiveness and grace; you guys don't have any of that."
Gill then went towards a man carrying a couple of religious-themed billboards and said, "You're a big dips---, you know that don't you?'"
Check out the video below: