The Greek verb agalliaō means to exult, leap for joy, or rejoice greatly — a word that goes beyond ordinary joy (chairō) to describe ecstatic, overflowing delight. It occurs about 11 times in the New Testament and has deep roots in the Septuagint's translation of Hebrew joy vocabulary.
Agalliaō describes the kind of joy that overflows all restraint. It is the joy of Mary in the Magnificat: 'My spirit rejoices (agalliaō) in God my Savior' (Luke 1:47). It is the joy of the disciples on the eve of Pentecost: eating together 'with glad and sincere hearts' (Acts 2:46). Peter uses it for the paradoxical joy of believers who suffer for Christ: 'you rejoice with an inexpressible and glorious joy' (1 Peter 1:8). This word insists that Christian joy is not manufactured positivity but the spontaneous overflow of souls that have encountered the living God. It is often linked with the Holy Spirit and eschatological hope.