How can we continue to run the race of the Christian life?

I am sure many of you have seen this — may be in your life or the life of others. Somewhere along the way something happens, that hinders you from running the race of the Christian life. The opposition beats you down with persecution. Your affections drift from Jesus to the things of this world. Your sinful nature wins out and you succumb to temptation. How can we keep this from happening? How can we continue to run the race of the Christian life so that we finish?