Global Missions - David Platt, John Piper

I've been reading through John Piper's free e-book When The Darkness Will Not Lift, which I intend on writing about soon, once I've processed the information.  However, a particular passage stood out for me, and relates very well to some other things I've been thinking about lately:

"What one thing comes to your mind from sixty years of ministry as to what Christians should do to increase their joy?  Almost without hesitation he said, 'Share their faith.'  Joy in Christ thrives on being shared.  That is the essence of Christian joy; It overflows or dies".