David Powlison, in his article “The Pastor as Counselor,” recommends these seven books for pastors who want to strengthen their counseling ministry:
Pastoral Care by Gregory the Great
Pastoral Counsel by Thomas Oden
Life Together by Dietrich Bonhoeffer
Powlison also recommends reading fiction because, “Good fiction gives you vicarious experience of people. It builds your case wisdom far beyond the bounds of your own social setting.” He suggests:
Cry, the Beloved Country by Alan Paton
Gilead by Marilynne Robinson
(And if you want to get into reading fiction in order to benefit your pastoral ministry, you should check out Pastors in the Classics: Timeless Lessons on Life and Ministry fron World Literature by Leland Ryken, Philip Ryken, and Todd Wilson).