10 We begin the holy fast on the fifth day of Pharmuthi (March 31), and adding to it according to the number of those six holy and great days, which are the symbol of the creation of this world, let us rest and cease (from fasting) on the tenth day of the same Pharmuthi (April 5), on the holy sabbath of the week. And when the first day of the holy week dawns and rises upon us, on the eleventh day of the same month (April 6), from which again we count all the seven weeks one by one, let us keep feast on the holy day of Pentecost— on that which was at one time to the Jews, typically, the feast of weeks, in which they granted forgiveness and settlement of debts; and indeed that day was one of deliverance in every respect.
Let us keep the feast on the first day of the great week, as a symbol of the world to come, in which we here receive a pledge that we shall have everlasting life hereafter. Then having passed hence, we shall keep a perfect feast with Christ, while we cry out and say, like the saints, 'I will pass to the place of the wondrous tabernacle, to the house of God; with the voice of gladness and thanksgiving, the shouting of those who rejoice;' whence pain and sorrow and sighing have fled, and upon our heads gladness and joy shall have come to us! May we be judged worthy to be partakers in these things.
Source: Letters (New Advent)