"Rejoice in the Lord alway: and again I say, Rejoice." (Philippians 4:4). God is full of joy. Jesus is a man full of joy. If we are going to follow after Him, we must be full of joy. What does that joy do? "...for the joy of the Lord is your strength." (Nehemiah 8:10).
The Apostle Paul conveyed the link between joy and strength. He knew that our faith is a violent force, that's why he said, "Fight the good fight of faith!" (1 Timothy 6:12). Paul recognized that our faith must be aggressive, and faith uses the Word of God as a weapon against demonic obstacles in its path. Therefore we cannot live by faith without joy, because it takes supernatural strength to live by faith. We are surrounded by a world that is flowing downstream towards death; its natural flow is always negative. To move toward life, we must constantly swim upstream. If we ever get too weak spiritually to swim upstream, we will find ourselves being swept back toward sickness, lack, or some other form of defeat. We cannot afford to run out of strength.
The Apostle Paul understood the link between joy and strength: he wrote "Rejoice in the Lord always!" Rejoice means to be full of joy, to be excited! Never lose your joy... never lose your excitement. Because when we do we will also lose our strength and suffer lack, become sick, and defeated. Read, study and meditate on Colossians 1:11. The true heart of that says we are strengthened with God's power, His might, to endure with joyfulness. Paul affirmed that which was true in Nehemiah's day under the Old Covenant, is also true under the New Covenant. "The joy of the Lord is our strength!" In order for us to remain strong spiritually we MUST remain joyful. Confess "I rejoice in the Lord always!"