The fish represents a lifestyle of evangelism. Go back to your Sunday School songs about "fishers of men" and you'll connect this image correctly. Right thinking about evangelism is pretty widespread. Most everyone knows of the need for it, but it is so rarely done. How can we motivate ourselves in this area? Instead of the "guilt trip" approach, let's imagine what it would be like to join in the celebration of having found that which was lost. This is the Bible's idea of ultimate happiness. Three parables in Luke confirm this overarching theme from the whole of Scripture. 
The sheep is a picture of our ministry of discipleship. My wife's uncle owns a sheep farm in Southern Ontario, Canada. When we've been through their barn in the past, we've been greeted by the sheep as though we were aliens from outer space. They consider us to be complete strangers. It's an amazing picture of John 10. Anyway, the idea is that we are to train ourselves (and others) to follow only one Voice. All others should be alien to us.
An old African story tells about the day of a large feast. The tribal chief asks various animals what they can provide in order to make the celebration possible. The cow can give milk (so can the goat if you prefer!). Many other helpful contributions are made by the time he comes to the chicken. "I can lay some eggs," says the chicken cheerfully. Involvement. This is the next stage... alongside evangelism and discipleship comes involvement. Many believe that this is the last stage, but we are called further. No mere token offering of ourselves will suffice. 
The chief commends the chicken for her involvement and turns to the pig. "What can you provide for the feast?" The pig replies, "If I am to offer anything, it will cost me everything. It will be my life that I give." And we arrive at the point of Christian maturity. Evangelism will emerge from it. Discipleship is dependent upon it. And involvement inevitably springs out of it: self-sacrifice. It's here where we begin to mimic the Divine Life, marked even within the Trinity by self-giving. So we can ask ourselves, "How much of me is for the Kingdom?" By doing so, we will ultimately arrive at the level of our spiritual maturity. But just a word of caution. Let this self-examination be one of joy and not guilt. As we look inward, let it be with a desire for abiding in Christ instead of working for Him. The relationship we then find will provide abundant motivation for the Christian life.
You'll probably remember these four animals when you wake up in the morning... maybe even for the rest of your life! Fish... Sheep... Chicken... Pig.
