Oak Tree or Acorn?

Why is it that Christians seem to be so content with so little of what Jesus offers. Its kind of like an acorn being content with being an acorn though it knows that it could be an oak tree. Jesus said, "I tell you the truth, anyone who has faith in me will do what I have been doing. He will do even greater things than these, because I am going to the Father. And I will do whatever you ask in my name, so that the Son may bring glory to the Father. You may ask me for anything in my name, and I will do it." John 14:12ff Do we really believe this? I sometimes think that when we don't see the power of God in healings, deliverance, or provision that we believe that Jesus must be kidding when he said the words above. Could it really be true that we could do 'greater things' than Jesus? The context here is clearly referring to the miracles Jesus did. Maybe we don't see 'greater things' because  we don't really take Jesus at His word, even if we took Him at His word we don't expect Him to do them through us and because maybe He knows that all to often we would steal His glory if He did do them through us. So we go on living an acorns life when we could become the oak tree God created us to be.