Gretta has served West Hill United in Scarborough, Ontario, for nearly two decades. She helped transition the church to a secular community. She is the author of the national bestseller, With or Without God: Why the Way We Live is More Important that What We Believe, and Amen: What Prayer Can Mean in a World Beyond Belief. Gretta founded the Canadian Centre for Progressive Christianity, and served as a Director and Officer of The Clergy Project. Gretta also serves as a Vice-Chair of the Board of Governors of Centennial College.