The joy of the Lord is a great source of strength. It is a gift from God. Human joy can’t take us very far. It disappears in the dark shadows of our trials and tribulations, but the joy which God gives by the Holy Spirit is permanent and as eternal as the life God has given us through Christ.
Prior to Jesus going to the cross and returning to the Father, He told His disciples:

“Until now you have asked nothing in my name. Ask, and you will receive, that your joy may be full” John 16:24
He also said,
“you have sorrow now, but I will see you again, and your hearts will rejoice, and no one will take your joy from you” (John 16:22).
“If you abide in me, and my words abide in you, ask whatever you wish, and it will be done for you. By this, my Father is glorified, that you bear much fruit and so prove to be my disciples.” John 15:7-8
“These things I have spoken to you, that my joy may be in you, and that your joy may be full.” John 15:11
The psalmist understood that joy did not from a human source, but from God:
“You have put more joy in my heart than they have when their grain and wine abound” Psalm 4:7
What God puts there, stays there. Every person who trusts in Christ will experience persecution, trials, and tribulations, but the believer does not have to base their joy upon circumstances. They’ve learned, like the Apostle Paul, to be content in all circumstances (Philippians 4:11-13). Paul’s contentment rested in Christ, not in circumstances. He knew that God does not change, so Paul’s contentment remained.
James also tells us to consider trials with all joy.
“Count it all joy, my brothers, when you meet trials of various kinds, for you know that the testing of your faith produces steadfastness” James 1:2-3
How about David:
“You make known to me the path of life; in your presence there is fullness of joy; at your right hand are pleasures forevermore.” Psalms 16:11
Joy is contagious. When someone around you is joyful, it’s hard not to notice, but the most powerful thing about joy is that it’s a source of strength for us. Joy is a natural byproduct of being chosen by God; being saved by God; and having God’s Spirit live within us. Joy is also a fruit of the Holy Spirit. Paul writes that “the fruit of the Spirit is love, joy, peace, patience, faithfulness, kindness, gentleness, goodness, self control. (Galatians 5:22), so joy is a gift from God; joy is a source of strength; and joy is a fruit of the Spirit. We can also consider the tests, trials, and tribulations as joy, knowing the end result. And finally, joy is good for us and good for those around us. Our secure standing before God in Christ ought to fill us with joy, because now, there is no more condemnation for those who are in Christ (Romans 8:1). What could be better than all of that!?
adapted from the article How Joy Is A Source of Strength June 5, 2019, by Jack Wellman http://www.patheos.com