We know that we have a vocation when we spend years thinking it through, preparing our way forward by reading and reflection and with conversation. Vocation does not come automatically when the drunkard, who I doubt ever had a serious thought in his head, has an emotional rush and decides to tread the straight and narrow. Good for him, but it does not make him a world leader. While fundamentalist Christianity believes that the conversion experience makes a new man, we know that personality changes only gradually over a lifetime.
In the circles I grew up around (a Presbyterian among Southern Baptists in East Texas), what I have to say would be called a "testimony," but I don't mean it like that. However, I come to my present religious convictions after a long effort, not a sudden "conversion." Not that I disdain conversions; that's another topic altogether. But I don't think much of suddenly becoming a "new person," either.
When I was in high school, the favorite question put to me by concerned classmates (their concern was a theological matter; we'll have to get to that, too, by and by) was: "Are you saved?" To which I could only honestly answer: "Well, I hope so." I didn't figure I could enforce any contract with God, if God decided not to fulfill God's obligations. But I also, instinctively almost, distrusted any assurance that whoever and whatever I was could be wiped away with a moment's decision. Besides, I could never understand quite what was meant when they said I had to "let Jesus into my heart." The phrase just had no real meaning for me; and still doesn't.
My calling as a pastor came over a long period of time: after a Master's in English, after law school and a legal career, after it seemed too late and too hard to start over a third time, and go to graduate school once more. It came after a period of long consideration, and even longer preparation. And then becoming a pastor was another period of change, of slow sculpture: a continuation of a process, perhaps, but an unfinished process, to be sure. Still, this isn't about me; it's about conversion.
My experience rings true with Sellick's statement: conversion comes over time. Vocation is something you pursue, just as Christian mystics and religious (those who commit themselves to following a Christian life as a vocation, not just an avocation) have always done. It is not an emotional event, as sudden as Paul's experience on the road to Damascus. It is a gradual change, over time. Even Peter struggled with the gospel he was supposed to proclaim. In Acts, he is depicted having trouble reconciling the revelation to him, with his knowledge of Jewish law. He remains convinced his knowledge is "the real deal," and has trouble accepting what he has seen and heard. To this day, there is a division in Christianity between Peter and Paul, but one that is to be expected. Still, neither Peter nor Paul changed suddenly, or even completely, and knew all they needed to know from a point in time, forward.
That is the first error of simplifying Christianity to the point that it is simply a series of dictates, of "Thou Shalt Nots" that will correctly guide your every action. It's a question of journey, not of arrival.
There's a lot to consider in this Sellick article. If I didn't have to do yard work now, I'd pursue a bit more of it.