Every account of our Lord's Ascension contains also His final instructions to the Apostles, traditionally called the Great Commission (cf. Mt 28:16-20; Mk 16:14-18; Lk 24:44-49; Acts 1:4-8). When He ascended He did not simply say to His Apostles, "Wait here until I get back." On the contrary, He put them — and us — to work. And this commissioning is not incidental to His Ascension, as a last minute decision perhaps. Rather, He ascends to the Father so that He can continue His work in the world through us. So we do not merely await our Lord's return; we labor on His behalf until He comes to bring all things to completion.
Now before we can get to work, we need to know what the work is. Before we can be commissioned, we need to know the mission. So before His Ascension our Lord provides a summary of what He accomplished: "Thus it is written that the Christ would suffer and rise from the dead on the third day" (Lk 24:46). Of course, this is not all that He did. But it is the essence of His mission and therefore of the Gospel: His suffering, death and resurrection. Everything else — His teachings, healings, preaching, etc. — point to and prepare for this, and have meaning only because of it.
Then our Lord makes known the continuing nature of His mission: namely, "that repentance, for the forgiveness of sins, would be preached in his name to all the nations, beginning from Jerusalem" (Lk 24:47). By His death and resurrection Christ has won for us heaven and all the graces necessary to get there. But His mission does not end with that. His truth and grace must be communicated to every soul throughout the world and throughout time. And there is no vehicle for this work except the Church. Through the Church our Lord extends Himself to all nations, making present and effective the graces He won for us.
His next words carry all the force of a commissioning: "You are witnesses of these things" (Lk 24:48). He is not just making an observation or merely stating a fact about the Apostles. He is identifying who they are, and therefore what they are to do. Since they are witnesses, they must bear witness. They are to testify to His truth. And so they did. They witnessed by the sacrifice of their lives. Indeed, the Greek word for witness — martyr — has become synonymous with such testimony.
"You are witnesses of these things." By extension, this charge applies to all Catholics. We are all witnesses. Not eyewitnesses, as were the Apostles, but witnesses nonetheless. By faith in the apostolic witness we know what they saw with their own eyes. We share in their knowledge of all that Christ said and did. And because we are witnesses we, like them, must bear witness.
Finally, our Lord instructs the Apostles, "I am sending the promise of my Father upon you" (Lk 24:49). He has given the commission, now He promises the means to accomplish it: the Holy Spirit. For no one can bear witness to our Lord unless the Holy Spirit enables Him. "No one can say 'Jesus is Lord' except by the Holy Spirit" (1 Cor 12:3). The task of Christian witness exceeds our human capacity. It comes only from our union with the Holy Spirit. And here we touch on the distinctive nature of Christian witness. We are not just representatives pointing to our Lord. Rather, the promise of the Father brings Christ to life within us, making us Christians — other Christs — in the world.
Further, just as the Holy Spirit transforms each of us, so also it quickens the Church, Christ's Mystical Body. The Church is not just a human institution established for liturgical and charitable purposes. Rather, because she has His Holy Spirit as her very soul, the Church is our Lord's continuing presence in the world. In a sense, she is Christ Himself. Through her He continues to teach, rule and sanctify. And by receiving her teachings, her instructions and her sacraments we become, with the Apostles, witnesses to the world.
