Some years ago we had a lot of denominational leaders visiting the campus where I teach. In one meeting with the faculty, we went around the room and asked this diverse group about their call to the ministry. Some of them had some extraordinary experiences. For others, it had been a fairly cerebral thing. But as I listened to the denominational leaders and then faculty, do you know what I found in common without a single exception? Each one of them would speak of a text that had just leaped off the page and grabbed them by the throat and wouldn't let go.
What was common in all of them was a profound, unswerving, immutable passion that believed the gospel is so central in all of human life that nothing in comparison with its proclamation is worth doing.
Not for a moment am I saying God doesn't call some Christians to be chemists or others to be garbage collectors. But you will find in the proclaimers of God's message those who sense a call upon their lives. You will find without exception they have this sense of the sheer non-negotiable value of the gospel.