While searching online for information written on the call to preach, I found this three-part series at 9Marks. It was written by Bobby Jamieson, of whom the blurb says is a PhD student in New Testament at the University of Cambridge, and had served as assistant editor for 9Marks. Linking this series is not an endorsement of all the views of Jamieson, but I think you will find it interesting. I hope to follow up with something of my own on the subject.
The Double Presumption of Calling to Ministry -- "Calling language typically refers to a sense of divine guidance: “I think God is calling me to do this”."
Eldering, Economics, and Calling to Ministry -- "But there’s a wrinkle in this fabric: not all elders are paid, so not all elders serve full-time. In fact, Paul commended his own example of bi-vocational ministry to the Ephesian elders."
Reframing “Calling”: Words to Churches and Aspiring Pastors -- "I think one of modern evangelicals’ most damaging, widespread assumptions is that the only real ministry is done by those who do it full-time."