Joy

The mark of the believer, individually and corporately. A quality, not simply an emotion, grounded and derived from God (Psalm 16:11, Phil 4:4), which characterises the Christian life (1 Peter 1:8), and anticipating the joy of being with Jesus forever in Heaven. The gospels speak with joy of the proclamation of the good news, that the Kingdom of God has come and is open to all who repent and believe! And John speaks of joy flowing from a deep fellowship between the church and Jesus. Paul uses the term in 3 ways:

1. as fellow Christians grow in Christ -particularly the ones he himself led to Christ- it is a cause for joy.
2. Christian joy might paradoxically be an outcome of suffering, and experiencing sorrow for Christ's sake.
3. Joy is a fruit of the Spirit. As a fruit of the Spirit, it can be interrupted by sin and so all believers are called upon to share in the joy of Christ by a daily walk with Him and a daily practice of rejoicing in the knowledge of Him and his salvation (Phil. 3:1, 4:4, 1 Thess. 5:16)
The New Bible Dictionary (summary)