Does it seem that there is more reason for sorrow than for joy? 
There's not.

Am I ignoring the pain and suffering which is so prevalent in life?
I'm not. It sucks. We should rely on our JOY as we combat those things.

How can there be anything to rejoice about when there is war, injustice, people being falsely accused and condemned, people taking advantage of others for their own benefit, people working to bring misery on others, people living in fear?
Because JOY is GREATER than that. 

The reasons for joy are GREATER than the reasons for giving up. And the JOY that will sustain you comes from a source which is greater than any misery the world can muster. And you can count on it at all times and in every way.