John 1:8 says, 'He was not the light, but came to bear witness about the light.'
He is referring to John the Baptist.
I listened to Rob Bell's latest sermon last night entitled ' God Wants to Save Christians Part 2' and that sermon goes well with this verse.
What Rob talks about is that all we are called to do is to demonstrate, then explain and then leave. We are to demonstrate God's power through changed lives and when people ask where that comes from we explain it and then if they aren't interested we simply leave. We don't stay and harrass them.
John was not the light just like we are not the light. What we are, are people that the light has come into. We were born into flesh and sin, but God has forgiven us and come into our lives.
We are to bear witness at the light in our lives.
Rob goes onto say how we are not supposed to prove why everyone else is wrong, but to simply show (not talk) the power of God in our lives and to have an explanation for why we have been able to overcome darkness.
Some people haven't let the power of God into their lives and so they only know God with their minds. This leads them to prove to others how right they are and how wrong everyone else is. God is a God of experience and when we interact with him from a humble stance we can't help but to be changed.
We are not the light, but God is the light and we are to bear witness to it.