Mast was the author of six books on Christian practice and theology, and the editor of a collection of sermons by Reformed minister and theologian Howard G. Hageman From 2006 to 2017,[2] Mast served as the fourteenth president of the New Brunswick Theological Seminary located in New Brunswick, New Jersey, in the United States—one of two seminaries affiliated with the Reformed Church in America.

[5] This move—part of a large-scale redevelopment of the College Avenue area of New Brunswick by New Brunswick Development Corporation (DEVCO), Rutgers University and the seminary—was made in response to the seminary's declining enrollment, financial constraints and to replace an aging campus with a modern, environmentally-friendly campus.

[3] His doctoral dissertation was titled The Eucharistic Service of the Catholic Apostolic Church and Its Influence on Reformed Liturgical Renewals of the Nineteenth Century (1985) which was later published as a book in 1999.

[3] Mast has served congregations in Johannesburg, South Africa, in Newark and Irvington in New Jersey, and Albany, New York.

[8][9] He notably said, "Worship leaders need to strive for a tone that is both relevant and dignified, personal without being private, expressive as well as evocative, and contemporary while embracing the eternal.