As believers in the good news of the Gospel, Christians respond with joy to the salvation event accomplished by Jesus Christ. Joy is inseparable from Christian faith - for those who believe, it is a not a possibility but a responsibility. The responsibility of joy descends from the Paschal event, in which God raised Jesus Christ and revealed to humanity the hope in the resurrection. The entire Gospel unfolds between the announcement of the great joy of the Savior's birth in Bethlehem (Cf. Luke 2:10-11) and the explosion of joy at dawn on the first day after the sabbath, the day of the resurrection (cf. Matthew 28:8). If we want to understand what it means to say that Christian life is joyful, we should ask ourselves what joy is in human experience. We may not manage to define it perfectly, but each of us has experienced joy. It is like a peak moment in our life, a sensation of fullness in which life seems positive, meaningful and worthy of being lived. With Hans Georg Gadamer we can call joy a revelation: "Joy is not simply a condition or a feeling; it is a sort of manifestation of the world. Joy reveals itself in our discovery that we are satisfied."
In the experience of joy, our daily life undergoes a kind of transfiguration. The world gives itself to us, and we enter into joyful gratitude: "The only relationship between consciousness and happiness is gratitude" (Th. W. Adorno). We are grateful because we are joyful. Joy is the experience of meaningfulness that opens the door to our future by giving us hope. It implies a relationship with time: there is the joy of waiting (for the arrival of someone we love, for a birth, etc.), the joy of someone's presence, and the joy of remembering (or, if we prefer, the memory of joy - as we remember, we re-live the joy we have experienced in the past). This is especially evident during moments of celebration, when we experience the joy of being together - when does a celebration start, and when does it end? This is not easy to say, because it already exists in the joy of those who prepare it and wait for it to begin, and it continues to exist in the joy of those who remember it. Joy is also connected to meeting others and to our positive experience of their presence. The words of greeting used by many cultures are significant: the Greek chaîre (literally, 'rejoice') wishes the other person joy at the moment of meeting, and the Hebrew shalom (and related terms in other Semitic languages) also wishes the other person a situation in which he or she might experience joy.
We can say, in summary, that joy is an experience that embraces our entire existence, and that makes itself felt with force in moments of love (the joy of friendship and love) and at times of celebration (sharing a meal together is a celebration par excellence of the joy of living, and of living together). We cannot fail to see that these dimensions of joy take on their full meaning in Christ, during the celebration of the Eucharist. It is "with joy" that we give thanks ("Give thanks to the Father with joy," cf. Colossians 1:12), and the Eucharist is the joy of remembering the Paschal event, which we re-live in the present, and the joy of waiting for its eschatological fulfillment when the Lord comes in glory. It is also the joy, expressed in particular through the 'holy kiss,' of the communion that the presence of Christ creates among those gathered together: "Seeing everyone together at the Eucharist is a source of overflowing joy" (Jerome). This joy "in Christ" is a joy that is extremely human - its physical dimension is never excluded, we express it in our human relationships, and it culminates in the Eucharistic meal, where the celebratory symbol becomes, in Christ, a prophecy of the eschatological banquet. The eschatological dimension of Christian joy also takes the form of "joy in affliction" (2 Corinthians 7:4, Colossians 1:24) - in other words, joy that does not disappear even in situations of suffering and contradiction.
This does not mean, of course, that as Christians we no longer experience moments of sadness or pain that make joy temporarily impossible. These moments exist, but Christian joy continues to dwell in our inmost depths as part of our life hidden in God. It is the indescribable and glorious joy (1 Peter 1:8-9) of those who love Christ and already live with him in the secrecy of faith. It is the joy no one can take away from us, because no one can prevent a Christian from loving the Lord and his or her brothers and sisters even in situations of extreme suffering - the martyrs are there to remind us of this. Christian joy costs us a great deal because it means accepting our condition of temporality and mortality, but it allows us to make our inevitable descent towards death an ascent towards the Father. In our hope-filled journey towards our Lord, we look forward with joy to meeting the One whose face we have sought with longing during the days of our existence. This is why, in the New Testament, joy is an apostolic command: "Rejoice in the Lord always. I shall say it again: rejoice!" (Philippians 4:4). We can experience joy now, but there is also the fullness of joy that is to come, the joy of meeting the Lord face to face. If joy is our responsibility as Christians, we need to dedicate ourselves to practicing it - first, because this will help us defeat the spiritus tristitiae (spirit of melancholy) that always threatens us, and second, because we cannot deprive the world of our testimony of the joy whose source is faith. The joy of those who believe is what tells the world about the glory of God! This is what the world asks: "Let the Lord show his glory; and you, believers, show us your joy!" (cf. Isaiah 66:5).