St. Leo the Great: . . . For as of old on the fiftieth day after the Sacrifice of the Lamb, the Law was given . . .

Icon of Pentecost“. . . For as of old on the fiftieth day after the Sacrifice of the Lamb, the Law was given on Mount Sinai to the Hebrew people, now delivered from the Egyptians, so, after the Passion of Christ, in which the True Lamb of God was slain, on the fiftieth day after His Resurrection, the Holy Spirit descended upon the Apostles and upon the people who believed (Acts ii.3); so that an earnest Christian might know beyond any uncertainty, that the sacred rites of the Old Testament had served as foundations for the Gospel, and that by this same Spirit was the Second Covenant laid down, by Whom the first had been established.”

+ St. Leo the Great, “The Work of the Holy Spirit”