The Greek noun agalliasis (ἀγαλλίασις) means exultation, intense joy, jubilant rejoicing — a joy that overflows and cannot be contained. It comes from the verb agalliaō (G21, to exult, leap for joy). This is not quiet contentment but exuberant, leaping, shouting joy. The word appears 5 times in the New Testament and is used for: Mary's joy (Luke 1:44, 47), the joy of Messianic banquet (Acts 2:46), the joy of hearing the gospel (Acts 16:34), and the joy of standing before God's throne (Jude 24).
Agalliasis is the joy of those who encounter God's salvation. It is eschatological joy — the joy of the Kingdom breaking in. When Elizabeth's unborn baby leaped (skirtaō) at the presence of the Lord in Mary's womb, Luke records Elizabeth saying the baby leaped "with joy [agalliasis]" — the first Advent response to Christ was uncontainable physical rejoicing. Mary's Magnificat (Luke 1:47) uses it: "my spirit rejoices in God my Savior." Jude 24 places agalliasis at the eschatological finale: God presenting believers faultless before His throne "with great joy." This word catches the intensity of the joy that awaits — the full-throated, whole-body, eternal rejoicing of the redeemed in God's presence. Christian joy is not shallow happiness but the first installment of eternal exultation.