From: Matthew 28:16-20
Appearance in Galilee. The Mission to the World
 Now the eleven disciples went to Galilee, to the mountain to which Jesus had directed them.  And when they saw him they worshipped him; but some doubted.  And Jesus came and said to them, "All authority in heaven and on earth has been given to me.  Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit,  teaching them to observe all that I have commanded you; and lo, I am with you always, to the close of the age."
16-20. This short passage, which brings to a close the Gospel of St Matthew, is of great importance. Seeing the risen Christ, the disciples adore him, worshipping him as God. This shows that at last they are fully conscious of what, from much earlier on, they felt in their heart and confessed by their words--that their Master is the Messiah, the Son of God (cf. Mt 16:18; Jn 1:49). They are overcome by amazement and joy at the wonder their eyes behold: it seems almost impossible, were he not before their very eyes. Yet he is completely real, so their fearful amazement gives way to adoration. The Master addresses them with the majesty proper to God: "All authority in heaven and on earth has been given to me." Omnipotence, an attribute belonging exclusively to God, belongs to him: he is confirming the faith of his worshippers; and he is also telling them that the authority which he is going to give them to equip them to carry out their mission to the whole world, derives from his own divine authority.
On hearing him speak these words, we should bear in mind that the authority of the Church, which is given it for the salvation of mankind, comes directly from Jesus Christ, and that this authority, in the sphere of faith and morals, is above any other authority on earth.
The Apostles present on this occasion, and after them their lawful successors, receive the charge of teaching all nations what Jesus taught by word and work: he is the only path that leads to God. The Church, and in it all Christian faithful, have the duty to proclaim until the end of time, by word and example, the faith that they have received. This mission belongs especially to the successors of the Apostles, for on them devolves the power to teach with authority, "for, before Christ ascended to his Father after his resurrection, he [...] entrusted them with the mission and power to proclaim to mankind what they had heard, what they had seen with their eyes, what they had looked upon and touched with their hands, concerning the Word of Life (1 Jn 1: 1). He also entrusted them with the mission and power to explain with authority what he had taught them, his words and actions, his signs and commandments. And he gave them the Spirit to fulfill their mission" (John Paul II, "Catechesi Tradendae", 1). Therefore, the teachings of the Pope and of the Bishops united to him should always be accepted by everyone with assent and obedience.
Here Christ also passes on to the Apostles and their successors the power to baptize, that is, to receive people into the Church, thereby opening up to them the way to personal salvation.
The mission which the Church is definitively given here at the end of St Matthew's Gospel is one of continuing the work of Christ--teaching men and women the truths concerning God and the duty incumbent on them to identify with these truths, to make them their own by having constant recourse to the grace of the sacraments. This mission will endure until the end of time and, to enable it to do this work, the risen Christ promises to stay with the Church and never leave it. When Sacred Scripture says that God is with someone, this means that that person will be successful in everything he undertakes. Therefore, the Church, helped in this way by the presence of its divine Founder, can be confident of never failing to fulfill its mission down the centuries until the end of time.
Source: "The Navarre Bible: Text and Commentaries". Biblical text taken from the Revised Standard Version and New Vulgate. Commentaries made by members of the Faculty of Theology of the University of Navarre, Spain. Published by Four Courts Press, Kill Lane, Blackrock, Co. Dublin, Ireland. Reprinted with permission from Four Courts Press and Scepter Publishers, the U.S. publisher.