In his book titled From the Resurrection to His Return: Living Faithfully in the Last Days, he recounts the following experience:
As a chemistry undergraduate at McGill University, with another chap I started a Bible study for unbelievers. That fellow was godly but very quiet and a bit withdrawn.
I had the mouth, I fear, so by default it fell on me to lead the study. The two of us did not want to be outnumbered, so initially we invited only three people, hoping that not more than two would come. Unfortunately, the first night all three showed up, so we were outnumbered from the beginning.
By week five we had sixteen people attending, and still only the initial two of us were Christians. I soon found myself out of my depth in trying to work through John's Gospel with this nest of students. On many occasions the participants asked questions I had no idea how to answer.
But in the grace of God there was a graduate student on campus called Dave Ward. He had been converted quite spectacularly as a young man. He was, I suppose, what you might call a rough jewel. He was slapdash, in your face, with no tact and little polish, but he was aggressively evangelistic, powerful in his apologetics, and winningly bold. He allowed people like me to bring people to him every once in a while so that he could answer their questions. Get them there and Dave would sort them out!
So it was that one night I brought two from my Bible study down to Dave. He bulldozed his way around the room, as he always did. He gave us instant coffee then, turning to the first student, asked, 'Why have you come?' The student replied, 'Well, you know, I think that university is a great time for finding out about different points of view, including different religions. So I've been reading some material on Buddhism, I've got a Hindu friend I want to question, and I should also study some Islam. When this Bible study started I thought I'd get to know a little more about Christianity - that's why I've come.'
Dave looked at him for a few moments and then said, 'Sorry, but I don't have time for you.'
'I beg your pardon?' said the student.
'Look,' Dave replied, 'I'll loan you some books on world religions; I can show you how I understand Christianity to fit into all of this, and why I think biblical Christianity is true - but you're just playing around. You're a dilettante. You don't really care about these things; you're just goofing off. I'm a graduate student myself, and I don't have time - I do not have the hours at my disposal to engage in endless discussions with people who are just playing around.'
He turned to the second student: 'Why did you come?'
'I come from a home that you people call liberal,' he said. 'We go to the United Church and we don't believe in things like the literal resurrection of Jesus--I mean, give me a break. The deity of Christ, that's a bit much. But my home is a good home. My parents love my sister and me, we are a really close family, we worship God, we do good in the community. What do you think you've got that we don't have?'
For what seemed like two or three minutes, Dave looked at him.
Then he said, 'Watch me.'
As it happened, this student's name was also Dave. This Dave said, 'I beg your pardon?'
Dave Ward repeated what he had just said, and then expanded: 'Watch me. I've got an extra bed; move in with me, be my guest - I'll pay for the food. You go to your classes, do whatever you have to do, but watch me. You watch me when I get up, when I interact with people, what I say, what moves me, what I live for, what I want in life. You watch me for the rest of the semester, and then you tell me at the end of it whether or not there's a difference.'
The young man didn't take Dave up on that offer, but he did keep coming back to watch how Dave lived his Christian life. Eventually the young man came to Christ and went on to become a medical missionary.
Dr. Carson concluded what he learned from Dave's challenge:
A Christian is saying in effect: "I'm one poor beggar telling another poor beggar where there's bread. I drank deeply from the wellsprings of grace. God knows I need more of it. If you watch me you'll see some glimmerings of the Savior, and ultimately you'll want to fasten on him. Watch me."
(Big) Dave was right! There is a very real sense in all who follow Jesus Christ have emblazoned on their back a big sign that reads: “WATCH ME!” And indeed, the world does watch us. And it draws conclusions as to the authenticity of our faith by what they observe!
SOURCE: D. A. Carson, From The Resurrection to His Return: Living Faithfully in the Last Days (Scotland: Christian Focus Publications, 2010).
ALSO AVAILABLE ONLINE IN VARIOUS PLACES: See, for instance, https://blogs.thegospelcoalition.org/justintaylor/2010/07/12/imitate-me/.
D. A. Carson himself is a Research Professor at Trinity Evangelical Divinity School in Bannockburn, Illinois, with a long and distinguished career in Christian communication, having written scores of books and articles, a great many of which are in print.
More information on Dr. Carson himself is available here: https://divinity.tiu.edu/academics/faculty/d-a-carson-phd/.
TO LISTEN TO A 2008 SERMON CONTAINING THE STORY REFERENCED ABOVE, GO TO: http://resources.thegospelcoalition.org/library/biblical-authority-the-exclusive-authority-of-scripture-for-faith-and-practice-2-timothy-3-10-17.
LASTLY, AN ADAPTED VIDEO VERSION IS AVAILABLE AT: https://www.youtube.com/watch?v=mH6_5-bn4Jw. Be sure to watch to the very end.