14 Nor indeed would anyone disbelieve this who has heard and knows that Moses, when little in the eyes of men, and not yet of any account, was called from the bush which burned but was not consumed, or rather by Him who appeared in the bush, and was encouraged by that first wonder: Moses, I say, for whom the sea was divided, and manna rained down, and the rock poured out a fountain, and the pillar of fire and cloud led the way in turn, and the stretching out of his hands gained a victory, and the representation of the cross overcame tens of thousands. Isaiah, again, who beheld the glory of the Seraphim, and after him Jeremiah, who was entrusted with great power against nations and kings; the one heard the divine voice and was cleansed by a live coal for his prophetic office, and the other was known before his formation and sanctified before his birth. Paul, also, while yet a persecutor, who became the great herald of the truth and teacher of the Gentiles in faith, was surrounded by a light and acknowledged Him whom he was persecuting, and was entrusted with his great ministry, and filled every ear and mind with the gospel.
Source: Orations (New Advent)