The joy of the Lord is the joy of forgiven sin. This is the joy that Jesus gives that no one can take away. This is also the joy that is always there for you, always at your disposal. Life is full of challenges and hardships, but the promise of God in Jesus Christ is that if you confess your sins, He is faithful and just to forgive you and cleanse you from all unrighteousness.
If you do not have this persistent joy in your life, it may be because you are not a Christian and you are still in your sins, or it may be because you are a Christian, and you haven’t been confessing your sins and you’re out of fellowship with God and the people around you. John says that he wrote his letter so that we might have fellowship with him, and his fellowship is with the Father and the Son, and he says he wrote that our joy might be full. So joy goes together with fellowship, beginning with fellowship with God, and then flowing out into fellowship with those around you. Then it says that this fellowship and joy is light. God is fullness of joy and fullness of fellowship, and therefore He is light and there is no darkness in Him at all. Sin is darkness. Sin brings shadows, doubt, mistrust, misunderstanding, confusion, hurt, depression, sadness. If your heart is full of those things, if your home is full of those things, then it has darkness in it.
Then it says this: if we walk in the light as He is in the light, we have fellowship with one another, and the blood of Jesus Christ cleanses us from all sin. The way to walk in the light and be in fellowship with God and one another is through the blood of Jesus cleansing us from all our sin. How do we get the blood of Jesus to cleanse us? If we confess our sins, He is faithful and just to forgive us and cleanse us from all unrighteousness.
Forgiveness of sins is the foundation of Christian joy. You can face very difficult circumstances, even terrible and horrible things, but if your sins are forgiven, you won’t lose your joy. It is possible by the grace of God to always walk in the light, meaning that you determine to confess your sins as soon as they happen, as fast as possible, before the sun goes down every day, so that the blood of Jesus cleanses you right away, and you stay in fellowship and you never lose your joy.