A letter from Constantine to those assembled as delegates to the Council of Nicaea regarding Jewish Christians and the date of the celebration of Easter:
When the question relative to the sacred festival of Easter arose, it was universally thought that it would be convenient that all should keep it on one day; for what could be more beautiful and desirable than to see this festival, through which we receive the hope of immortality, celebrated by all in one accord, and in the same manner? It was declared to be particularly unworthy for this, the holiest of all festivals, to follow the custom (the calculation) of the Jews, who had soiled their hands with the most fearful of crimes, and whose minds were blinded. In rejecting their custom, we may transmit to our descendants the legitimate mode of celebrating Easter, which we have observed from the time of the Savior’s Passion to the present day (according to the day of the week). We ought not therefore to have anything in common with the Jews, for the Savior has shown us another way: our worship follows a more legitimate and more convenient course (the order of the days of the week); and consequently, in unanimously adopting this mode, we desire dearest brethren to separate ourselves from the detestable company of the Jews, for it is truly shameful for us to hear them boast that without their direction they could not keep this feast?… How, then, could we follow these Jews, who are most certainly blinded by error?… But even if this were not so, it would still be your duty not to tarnish your soul by communications with such wicked people (the Jews). Besides, consider well, that in such an important matter, and on a subject of such great solemnity, there ought not to be any division. Our Savior has left us only one festal day of our redemption, that is to say, of His holy passion, and He desired (to establish) only one Catholic Church. Think, then, how unseemly it is, that on the same day some should be fasting, while others are seated at the banquet; and that after Easter, some should be rejoicing at feasts, while others are still observing a strict fast. For this reason, Divine Providence wills that this custom should be rectified and regulated in a uniform way; and everyone, I hope will agree upon this point. As, on the one hand, it is our duty not to have anything in common with the murderers of our Lord, and as, on the other, the custom now followed by the Churches of the West, of the South, and of the North, and by some of the East, is the most acceptable, it has appeared good to all…You should consider not only that the number of churches in these provinces make a majority, but also that it is right to demand what reason approves…that we should have nothing in common with the Jews.
Eusebius, vita Const. 3.18-20