Below is my new favorite definition of joy.
What was the joy that Jesus had? Joy should not be confused with happiness...the joy of Jesus was His absolute self-surrender and self-sacrifice to His Father - the joy of doing that which the Father sent Him to do- "...who for the joy that was set before Him endured the cross..." (Hebrews 12:2). "I delight to do Your will, O my God..." (Psalm 40:8). Jesus prayed that our joy might continue fulfilling itself until it becomes the same joy as His.
Living a full and overflowing life does not rest in bodily health, in circumstances, nor even in seeing God's work succeed, but in the perfect understanding of God, and in the same fellowship and oneness with Him that Jesus Himself enjoyed. But the first thing that will hinder this joy is the subtle irratability caused by giving too much thought to our circumstances. Jesus said, "...the cares of this world,...choke the word and it becomes unfruitful" (Mark 4:19) And before we even realize what has happened, we are caught up in the cares.
"My Utmost for His Highest"