What does the Bible say about joy in the Christian life?

True joy in the Christian life is rooted in the joy of Jesus Christ, as stated in John 15:11, where Jesus desires that his joy might remain in us, resulting in our joy being full. This joy is not the same as happiness, which is based on external circumstances. Instead, joy is an internal state of being that remains even amidst trials and tribulations. Joy is a fruit of the Holy Spirit and is unique to believers, reflecting a deep relationship with God and assurance of His promises, such as those established in Romans 14:17 and Romans 15:13.