"...and last of all he appeared to me also, as to one abnormally born" (1 Corinthians 15.8).
In 1 Corinthians 15, Paul delineates the simple, all-sufficient truth of the gospel: the gospel is the death, burial, resurrection, appearances and ascension of Jesus Christ. Period.
But for Paul, when did the gospel become real? It wasn't real, producing grace and peace in his life, until Jesus appeared to him.
Throughout his letters, Paul typically has to defend himself in the face of trumped-up charges from his opponents. In Galatians, when those sympathetic to their Jewish roots charged that Paul's apostleship and gospel were fraudulent, Paul defended himself and his message by telling a story.
Galatians 1.10-2.10 is a story, a testimony from Paul, rooted in historical facts. Paul tells his story in three veins: pre-conversion, conversion, and post-conversion. He does so to uphold the sufficiency of the gospel and to defend his credentials as a bona-fide apostle of Jesus.
Have you ever written out the story of your salvation? Interestingly, when Jesus exorcised the demons from the man in the Gerasene region in Mark 5, he charged the newly-healed man to return home and tell his story to his family; to witness the qualitative difference God had made in his life (see Mark 5.1-20).
What we call "evangelism," Scripture calls "witnessing" (Notice in Acts 1.22 that in the search to replace Judas in the apostleship, the qualification is not someone who was an "eyewitness" of Jesus, as we often read verse 22, but someone who "must become a witness of his resurrection").
Becoming a witness is rooted in telling two stories: (1) The historical story of Jesus's all-sufficient power to save humanity; (2) The personal story of how Jesus saved you and transformed your life.
From both Jesus and Paul, I learn that the power of the gospel is not only found in the factual retelling of the historical story of Calvary but in the personal testimony of how Calvary makes a difference in my life.
What might help us in our quest to be more effective evangelists is an exercise that would be great, not only for those you seek to reach with the good news of Jesus, but also for yourself and your children. Write out your own conversion story. How has Jesus changed your life? Tell about your life pre-conversion. Tell about the moments surrounding the time when Jesus became real to you -- the critical understanding that led you to conversion and the confession that Jesus is Lord and Savior, the Son of God. Tell about your life post-conversion. How has obedient faith in Jesus made a qualitative difference in your life?
Taking the time to write out your story arms you with evidence of the difference Jesus can make the lives of those you seek to reach. Like the Samaritan woman who ran back into Sychar and told her friends about the difference Jesus had made in her life (see John 4), your friends and most especially, your children and grandchildren will appreciate knowing how the gospel has the power to change lives on a personal level.