In the early days of his Christian life, Os Guinness believed that he had to prove his commitment to Christ by becoming a minister or missionary. So, urged on by his spiritual mentors, he worked for a well-known church, but he was miserable. God changed his heart and refined his calling through a random encounter at a gas station. Here's how Guinness described it:

[In the days before self-service gas stations], I had just had my car filled up with gas and enjoyed a marvelously rich conversation with the pump attendant. As I turned on the key and the engine to [my car] roared to life, a thought suddenly hit me with the force of an avalanche: This man was the first person I had spoken to in a week who was not a church member. I was in danger of being drawn in a religious ghetto … . Ten minutes of conversation with a friendly gas pump attendant on a beautiful spring evening in [England], and I knew once and for all I was not cut out to [work full-time in a church].

Instead, as Guinness continued to pray and seek God's guidance, he discovered that God was calling him to work in the world so he could use his gifts and build relationships with people who didn't know Christ. After God released Guinness from what he was not supposed to do, Guinness found the freedom to pursue God's true calling for his life.