the moon, the apostolical tradition, which was preached at Rome by St. Peter, and confirmed at Alexandria by Mark the Evangelist, his interpreter, appointed that when the first month was come, and in it the evening of the fourteenth day, we should also wait for the Lord’s day, which falls between the fifteenth and the one-and-twentieth day of the same month. For on whichever of those days it shall fall, Easter will be properly kept on the same; as it is one of those seven days on which the unleavened bread is ordered to be kept. Thus it comes to pass that our Easter never deviates from the third week of the first month, but either observes the whole, or at least some of the seven legal days of unleavened bread. For though it takes in but one of them, that is, the seventh, which the Scripture so highly commends, saying, ‘But the seventh day shall be more solemn and holy, ye shall do no servile work therein,’ none can lay it to our charge, that we do not rightly keep our Lord’s Paschal day, which we received from the Gospel, in the third week of the first month, as the Law prescribes.
“The catholic reason of this observance being thus explained; the unreasonable error, on the other hand, of those who, without any necessity, presume either to anticipate, or to go beyond the term prescribed in the Law, is manifest. For they that think the Lord’s day of Easter is to be observed from the fourteenth day of the first month till the twentieth moon, anticipate the time prescribed in the law, without any necessary reason; for when they begin to celebrate the vigil of the holy night from the evening of the thirteenth day, it is plain that they make that day the beginning of their Easter, whereof they find no mention in the Law; and when they refuse to celebrate our Lord’s Easter on the one-and-twentieth day of the month, they wholly exclude that day from their solemnity, which the Law often recommends as memorable for the greater festival; and thus, perverting the proper order, they place Easter day in the second week, and sometimes keep it entirely in the same, and never bring it to the seventh day of the third week. And again, because they rather think that Easter is to be kept on the sixteenth day of the said month, and so to the two-and-twentieth, they no less erroneously, though the contrary way, deviate from the right way of truth, and as it were avoiding to be shipwrecked on Scylla, they run on and are drowned in the whirlpool of Charybdis. For when they teach that Easter is to be begun at the rising of the sixteenth moon of the first month, that is, from the evening of the fifteenth day, it is manifest that they altogether exclude from their solemnity the fourteenth day of the same month, which the Law firstly and chiefly recommends; so that they scarcely touch upon the evening of the fifteenth day, on which the people of God were delivered from the Egyptian servitude, and on which our Lord, by his blood, rescued the world from the darkness of sin, and on which being also buried, he gave us hopes of a blessed repose after death.
“And the same persons, taking upon themselves the penalty of their error, when they place the Lord’s day of Easter on the twenty-second day of the month, openly transgress and exceed the legal term of Easter, as beginning the Easter on the evening of that day in which the Law appointed it to be finished and completed; and appoint that to be the first day of Easter, whereof no mention is any where found in the Law, viz. the first of the fourth week. And they are sometimes mistaken, not only in defining and computing the moon’s age, but also in finding the first month; but this controversy is longer than can or ought to be contained in this letter. I will only say thus much, that by the vernal equinox, it may always be found, without the chance of an error, which is the first month of the year, according to the lunar calculation, and which the last. But the equinox, according to the opinion of all the Eastern nations, and particularly of the Egyptians, who exceed all other learned men in that calculation, usually happens on the twelfth day of the kalends of April, as we also prove by horological inspection. Whatever moon therefore is at the full before the equinox, being on the fourteenth or fifteenth day, the same belongs to the last month of the foregoing year, and consequently is not proper for the celebration of Easter; but that moon which is full after the equinox, or on the very equinox, belongs to the first month, and in it, without a doubt, the ancients were wont to celebrate the Passover; and we also ought to keep Easter when the Sunday comes. And that this must be so, there is this cogent reason, because it is written in Genesis, that ‘God made two lights; a greater light to rule the day, and a lesser light to rule the night.’ Or, as another edition has it, ‘A greater light to begin the day, and a lesser to begin the night.’ The sun, therefore, proceeding from the midst of the east, fixed the vernal equinox by his rising, and afterwards the moon, when the sun set in the evening, followed full from the midst of the east; thus every year the same first month of the moon must be observed in the like order, so that the full moon must be either on the very day of the equinox, as was done from the beginning, or after it is gone by. But if the full of the moon shall happen to be but one day before the time of the equinox, the aforesaid reason proves that such moon is not to be assigned to the first month of the new year, but rather to the last of the preceding, and that it is therefore not proper for the celebration of the Paschal festival.
“Now if it will please you likewise to hear the mystical reason in this matter, we are commanded to keep Easter in the first month of the year, which is also called the month of the new fruit, because we are to celebrate the mysteries of our Lord’s resurrection and our deliverance, with our minds renewed to the love of heavenly things. We are commanded to keep it in the third week of the same month, because Christ, who had been promised before the Law, and under the Law, came with grace, in the third age of the world, to be slain as our Passover; and rising from the dead the third day after the offering of his passion, he wished this to be called the Lord’s day, and the festival of his resurrection to be yearly celebrated on the same. For we also, in this manner only, can truly celebrate his solemnity, if we take care with him to keep the Passover, that is, the passage out of this world to the Father, by faith, hope and charity. We are commanded to observe the full moon of the Paschal month after the vernal equinox, to the end, that the sun may first make the day longer than the night, and then the moon may afford the world her full orb of light; inasmuch as first ‘the sun of righteousness, in whose wings is salvation,’ that is, our