"...For the joy of the LORD is your strength."

There is in this statement a truth, when established, confounds the world and upbuilds the church.
Ezra has just read to all the peoples the Law and all the peoples "were weeping when they heard the words of the Law.  
"This day is holy to the LORD your God; do not mourn or weep. For all the people wept as they heard the words of the Law."  Nehemiah 8:9
...And do not be grieved for the joy of the LORD is your strength."  Nehemiah 8:10b
(Read the verses 8-10 for the full picture.)

Jesus, the fulfillment of the Law,said,
"Abide in Me and I in you...."  John 15:4

"These things I have spoken to you, that My joy may be in you, and that your joy may be full."  John 15:11

No matter what circumstances surrounds the believer who sees God in all things and stands firm inn that knowledge, that one has 'joy unspeakable'.  It is that inner joy that shines through in quiet confidence, peace and strength.  It shows the world there is something different here and is attractive.

"A merry heart does good like medicine..." Proverbs 17:22

"A merry heart makes a cheerful face..."  Proverbs 15:13