Dr. Richard B. Gaffin, Jr. is the Charles Krahe Professor of Biblical and Systematic Theology at Westminster Theological Seminary in Philadelphia, Pennsylvania. He has taught at Westminster since 1965. He is an ordained minister in the Orthodox Presbyterian Church. He has written some extremely helpful books on the doctrine of salvation, such as Resurrection and Redemption: A Study in Paul’s Soteriology and By Faith, Not by Sight: Paul and the Order of Salvation. James Grant points to a great series of free audio messages by Dr. Gaffin on union with Christ. Here are the titles of the messages:
The Mystery of Union with Christ—Part 1
The Mystery of Union with Christ—Part 2
The Mystery of Union with Christ—Part 3
The Mystery of Union with Christ—Part 4
The Mystery of Union with Christ—Part 5
The Mystery of Union with Christ—Q & A, Part 1
The Mystery of Union with Christ—Q & A, Part 2