I was in a business meeting recently and someone was being praised. Their boss said to them that they had become the acceptable face of the company and known for delivering service.
That is, by their actions they had shown consistency, integrity and value. They had become the manifestation of the business' (good) reputation.
I believe that this is what evangelism is all about. Over the years I've heard evangelism 'repositioned' in the way people think of it and attempt it. Ultimately though, I think we have it a little backwards; putting the actions, be they relational or an event, first and the reason last.
Jesus didn't phrase it this way.
In John, chapter 17 is like a summary, where Jesus is praying about protection and the things to come. Chapter 18 then carries the story on to Jesus' arrest.
The above quote is just a small part of a fairly complicated chapter, but we can see a pattern that Jesus has set many times. That is; God first, the world second. As I commented here, Jesus summarised the Law as Love God then love the world. Our love with God produces an affect. Our relationship with God motivates (or at least it should.)
Jesus prays that we will be 'in' the Trinity as He is, and that He will be in us. Firstly Jesus just asks for that to happen then, secondly, He asks for it to happen so that the world would believe that Jesus had been sent by God. What reason does Jesus have for His first request? What comes before the need to prove who He was? See the pattern again?
Effective evangelism can only happen if we have God in us, and we are in God. It is the only way.
By being in and with God, we can be transformed into the manifestation of His reputation.