Ironically, this is a question that is asked, perhaps in different words, by those of us who too poorly represent the image of Jesus the Christ.
We've evangelized others even though:
. We had little idea what Jesus was like. We thought we could know Him without actually studying the documents that spoke about Him.
. We had almost no understanding of how the Old Testament related to the life of Jesus. At best we saw the Bible as a collection of unrelated stories.
. We thought that going to Church was enough to transform us into the character of Jesus. More Church = More Christian. Or so we thought.
. To say that we were ungracious and unloving toward those who believed and lived differently would have been a generous assessment of our character.
. We believed that being a follower of Jesus meant nothing more than not doing what sinners did.
If you want to evangelize, know your Saviour first.