While at Cambridge (1946–7) he attended lectures by
Ludwig Wittgenstein, which had a lasting impression on him, leading him to attempt a synthesis of the ideas of Wittgenstein and Aquinas. Ernst was significantly influenced by
Karl Rahner and acknowledged "my profound debt" to him. He produced the first English translation of Rahner's
Schriften zur Theologie which he penned the
foreword to and named
Theological Investigations. This title choice was influenced by Wittgenstein's book
Philosophical Investigations. Ernst edited a series of volumes entitled
Sacramentum Mundi: an Encyclopedia of Theology alongside Rahner and Kevin Smyth, and also Rahner and
Herbert Vorgrimler's
Theological Dictionary. A major focus of Ernst's work was on
grace. He edited and wrote the introduction to a Latin-English bilingual translation of the section on
grace in
Thomas Aquinas'
Summa Theologiae, which he published in 1972. In 1974 he published a book,
The Theology of Grace. He was a long time contributor to the
New Blackfriars journal. In 1979 many of his essays were posthumously published as a book,
Multiple Echo, featuring a foreword by
Donald M. MacKinnon. Ernst work influenced theologians
Nicholas Lash,
Fergus Kerr, and
Timothy Radcliffe. ==Bibliography==