The words “Repent! For the Kingdom of heaven is at hand!” were, according to Matthew 4:17, the first words of Christ’s ministry, symbolizing the simultaneous continuation and completion of St. John the Forerunner’s ministry (see Matthew 3:2), which was itself a continuation and completion of the prophetic ministry of all of the great figures of the Old Testament. It was with this message also that the Apostles began their ministry after the Ascension of Christ (see, for instance, Acts 2:38-39). Today, however, it is more often associated with the contemptible figure of the apocalyptic street preacher. It is a phrase that is actively avoided and even derided by more sensible Christians with a more sound approach to the faith. Unfortunately, so is active missionary work and anything resembling the apostolic mission to reach others with the Gospel message. I submit that this is largely because of our fundamental misunderstanding of the meaning of repentance, of conversion, and of mission.
The Apostles’ preaching was simple. What did they say, after all? One “Repent” followed by a “The Kingdom of God is at hand.” This was the Apostles’ preaching. What were the rest of the words? They were not words. They were that Wisdom which the Wisdom of Solomon mentions.
The proclamation is not a set of concepts, is not the contents of worldly human experience. These are human things that everyone knows. Rather, the proclamation is the experience and life of heaven; it is the revelation that accompanies that emigration to the life in heaven which the saints accomplish while they are still in this life. “The Kingdom of heaven is at hand” means that, indeed, it has come. It has come within me, within the apostle, within the saint. Thus only when I in fact possess Christ, possess the life and perception, the plenitude of the Kingdom, the fiery working of Heaven inside my heart, only then can I say: “Repent, the Kingdom of Heaven is at hand!” This is because “repent” means a complete change of heart, that is, a change in that spiritual faculty in the soul that comprehends heavenly things.
Without such lived experiences, without such charisms, generation after generation would not have been able to fill the world with the Orthodox faith. What can I say about what I have not seen? What shall I say if I do not have Heaven and the Kingdom within me? It is only thus that I know that Paradise exists and that I am able to tell others about it and how they may possess it. The work of a missionary is not therefore merely a struggle, a simple effort. It is a communication of Christ which must confront the dreadful egoism of men’s hearts. The missionaries, we might say, are obliged to confront heaven and earth, because man always rejects what is for his own good.
Archimandrite Aemilianos of Simonos Petras, “Second Sermon in Honor of Saint Herman of Alaska,” in Hieromonk Alexander (Golitzin), The Living Witness of the Holy Mountain: Contemporary Voices from Mount Athos, pp. 254-5