Proverbs 17:22 A merry heart does good like a medicine.  Merry also means blessed, glad, joyful and the word medicine can also be translated as cure.  So, a literal translation would be: “A merry, glad, joyful heart makes an excellent cure.”
Jesus joy was to be full and complete and perfect in us!  We are complete in Him.  We have His peace, we have His joy, we have His hope.  Wouldn’t Jesus be the ultimate cure for everything life throws at us?

The only side effect of this joyful heart is a voracious appetite. Jeremiah 15:16 says, “Your words were found, and I ate them, And Your word was to me the joy and rejoicing of my heart; For I am called by Your name, O LORD God of hosts.  Job esteemed the God's Word more than his necessary food.
 
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