Complex sentence: Erickson began teaching Canon Law and Church History at Saint Vladimir's Seminary in 1973 and became Dean in July 2002, following the retirement of Fr. Thomas Hopko, the first layman to hold the post.
Split into simpler sentences: Erickson began teaching Canon Law and Church History at Saint Vladimir's Seminary in 1973. Following the retirement of Father Thomas Hopko, he became Dean in July 2002, the first layman to hold the post.