Why do Orthodox Christians fast so much?

The reality is that we have fasting in the early church. One of the things that Christ said is, while I'm here, they will not fast, and while I'm gone, they will fast. One of the early Christian documents from the apostles is the Didache, and it literally says in the Didache that Christ instituted the Wednesday and Friday fast. But why do we fast? Fundamentally, fasting was seen as a way of strengthening our faith. When we are not being persecuted, we need to have challenges to strengthen us in our resolve to follow Christ. And so fasting is seen as a means of preparation to celebrate great events like the resurrection of Christ. We fast for forty plus days in order to prepare ourselves to celebrate that greater miraculous event. The same with the birth of Christ. It keeps us engaged in our faith.