One of the most important things that will sustain you in a life in ministry is the assurance of the call of God on your life.
"No one escapes the general call to mission. No one can say, ‘Witness is not for me.’ The critical question is not whether we’re called, for we are. The critical question is ‘Where am I called to?’ The answer may be to serve Jesus right where we are already, among those we live with and work beside. That is a wholly legitimate calling" (Alistair Brown, 1997).
I remember the moment that I was called to work with young people. It was a very profound experience that I will never forget. I believe that in order to make it for the long haul in ministry you need to point to a specific place in time where you were called to do what you are presently doing. There will always come a time when you will doubt that call out of distraction discouragement or disillusionment. We are all called to someone to somewhere and often times we miss that call because we are looking for something else.
When you are doing the most important thing on earth, working with kids. The devil will do whatever he can to get you to quit. What you have to do when that happens is remember to whom you are called.