Professor Mostert joined the Epworth Board of Management in November 2011. An Emeritus Professor of the University of Divinity, he was a minister of the Uniting Church in Australia for 39 years, exercising his vocation through congregational ministry, missionary service overseas and theological and ministerial education in various places.

Now officially retired, Professor Mostert was Professor of Systematic Theology in the Uniting Church Theological College, Melbourne for 17 years (teaching in the United Faculty of Theology), and before that in the United Theological College, Sydney. Professor Mostert continues to teach systematic theology at the Yarra Theological Union in Box Hill.

Professor Mostert has worked in inter-church dialogue at national level for many years and is a past President of the Australia and New Zealand Association of Theological Schools and of the Melbourne College of Divinity (now the University of Divinity). He was chair of the association that published the Australian theological journal, Pacifica. He was at different times a member of the Councils of Queen's and Ormond Colleges. He has edited and written several books and continues to publish essays as book chapters and in theological journals.