From The Gospel of Matthew, by Curtis Mitch and Edward Sri, commenting on Matthew 28:16-20
Every lifelong commitment must have a beginning. Discipleship begins with a sacramental initiation, with baptizing all new followers of Jesus in the name of the Father, and of the Son, and of the holy Spirit.
Although the doctrine of the Trinity would not be clearly articulated by the Church until the fourth and fifth centuries, the seeds of this teaching are present in this command of Jesus and in many other New Testament texts. Besides that, readers of Matthew first encountered the Father, Son, and Spirit in the context of Jesus’ own baptism (3:13–17). Thus the relationship of baptism to the three Persons of the Trinity does not come out of the blue, for they have already been linked together at that earlier point in the Gospel.
Along with baptism, new disciples are to be instructed in the teachings of Jesus. The importance of hearing Jesus’ words and putting them into practice, emphasized in the Sermon on the Mount (7:23–27), is here confirmed. Of course this will entail an introduction to basic principles and precepts, but eventually the disciple is to receive a full presentation of all that Christ commanded. The gospel is meant to give shape and direction to our entire life, so believers must be informed of how it impinges on family matters, economics, relationships, employment, government, education, and so on.
In other words, the good news of Jesus Christ must ultimately go beyond personal formation to a broader inculturation. The Lord wants the truth of his message to Christianize all nations as nations. Only when both individuals and societies are conformed to the gospel can we say that the Father’s will has been done “on earth as in heaven” (6:10).
The parting words of Jesus bring our minds back to the beginning of Matthew, where Jesus received the name Emmanuel, meaning “God is with us” (1:23). Here the same idea is expressed in the statement: I am with you always.
This is his promise to remain forever present with the Christian community (see 18:20). The disciples are not left to rely on their own resources as they march forth with the gospel. Jesus is there to unleash its power and to prepare the hearts of all who receive it. When the disciples proclaim the good news, it is the words of Jesus that the hearers accept or reject (see 7:24–27). When the disciples administer baptism, it is Jesus who baptizes “with the holy Spirit and fire” (see 3:11). It is the active presence of Christ that makes the Church the “universal sacrament of salvation” for the world.