“And these men, receiving in themselves the recompense of their error, when they place Easter Sunday on the twenty-second day of the month, openly transgress and do violence to the term of Easter appointed by the Law, seeing that they begin Easter on the evening of that day in which the Law commanded it to be completed and brought to an end; and appoint that to be the first day of Easter, whereof no mention is any where found in the Law, to wit, the first of the fourth week. And both sorts are mistaken, not only in fixing and computing the moon’s age, but also sometimes in finding the first month; but this controversy is longer than can be 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 must be the first month of the year, according to the lunar computation, and which the last. But the equinox, according to the opinion of all the Eastern nations, and particularly of the Egyptians,(966) who surpass all other learned men in calculation, falls on the twenty-first day of March, as we also prove by horological observation. Whatsoever 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 meet for the celebration of Easter; but that moon which is full after the equinox, or at the very time of the equinox, belongs to the first month, and on that day, without a doubt, we must understand that the ancients were wont to celebrate the Passover; and that we also ought to keep Easter when the Sunday comes. And that this must be so, there is this cogent reason. It is written in Genesis,(967) ‘And God made two great lights; the greater light to rule the day, and the lesser light to rule the night.’ Or, as another edition(968) has it, ‘The greater light to begin the day, and the lesser to begin the night.’ As, therefore, the sun, coming forth from the midst of the east, fixed the vernal equinox by his rising, and afterwards the moon at the full, when the sun set in the evening, followed from the midst of the east; so every year the same first lunar month must be observed in the like order, so that its full moon must not be before the equinox; but either on the very day of the equinox, as it was in the beginning, or after it is past. But if the full 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 meet for the celebration of the Paschal festival.