Professor Borgen introduces fresh perspectives into debates on central issues: assimilation and separation, mission and proselytism, John and the Synoptics, exegesis of the Old Testament, Jewish and Christian 'mystical' ascent and their religious and political functions. He explores the complexity of Judaism both in Palestine and in the Diaspora, and looks at the variety of tendencies which existed within Christianity as it emerged from Judaism and spread out into other nations.

In studies on Paul's letters and the Acts of the Apostles, he deals with catalogues of vices and the so-called Apostolic Decree, and on different views on the role of the reception of the Spirit by Christian converts. Finally, Professor Borgen draws on extensive material from Jewish sources to illuminate themes related to the Book of Revelation; and makes comparison between the reports by Philo and John the Seer on their own heavenly visionary ascents.