He earned both a Master of Divinity of degree and a Master of Theology degree from Westminster Theological Seminary. He earned his Doctor of Philosophy degree from Harvard University in 1945. He was originally ordained in the United Presbyterian Church of North America, then (due to church unions) with the United Presbyterian Church in the United States of America and the Presbyterian Church (USA). In 1990, he left the PCUSA for the Presbyterian Church in America.
Gerstner counted among his students, noted author and preacher, R. C. Sproul, founder of Ligonier Ministries, Dr. Arthur Lindsley, Senior Fellow at the C.S. Lewis Institute, and Dr. Walter (Wynn) Kenyon, Professor of Biblical Studies and Philosophy; Chair of the Philosophy Department and Division of Ministry and Human Services at Belhaven University.
In addition to the books Gerstner had written, he also recorded several lengthy audio courses giving a survey of theology, church history, and Christian apologetics, which are distributed through Ligonier Ministries. Gerstner was non-dispensationalist.
In 1976, a Festschrift was published in Gerstner's honor. Soli Deo Gloria: Essays in Reformed Theology included contributions by Cornelius Van Til, J. I. Packer, Philip Edgecumbe Hughes, John Murray, R. C. Sproul, John Warwick Montgomery, and Roger Nicole.
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