The Church requires that her children, at the very bare minimum, receives Holy Communion once a year, during Eastertide.
Dom Prosper Gueranger explains:
It was in the year 1215, in the 4th General Council of Lateran, that the Church, seeing the ever growing indifference of her children, decreed with regret that Christians should be strictly bound to Communion only once in the year, and that that Communion of obligation should be made at Easter. In order to show the faithful that this is the uttermost limit of her condescension to lukewarmness, she declares, in the same Council, that he that shall presume to break this law, may be forbidden to enter a church during life, and he deprived of Christian burial after death, as he would be if he had, of his own accord, separated himself from the exterior link of Catholic unity.
[Two centuries after this, Pope Eugenius the Fourth, in the Constitution Digna Fide, given in the year 1440, allowed this annual Communion to be made on any day between Palm Sunday and Low Sunday inclusively. In England, by permission of the Holy See, the time for making the Easter Communion extends from Ash Wednesday to Low Sunday].
These regulations of a General Council show how important is the duty of the Easter Communion; but, at the same time, they make us shudder at the thought of the millions, throughout the Catholic world, who brave each year the threats of the Church, by refusing to comply with a duty, which would both bring life to their souls, and serve as a profession of their faith. And when we again reflect upon how many even of those who make their Easter Communion, have paid no more attention to the Lenten Penance than if there were no such obligation in existence, we cannot help feeling sad, and we wonder within ourselves, how long God will bear with such infringements of the Christian Law?
The fifty days between Easter and Pentecost have ever been considered by the Church as most holy. The first week, which is more expressly devoted to celebrating our Lord’s Resurrection, is kept up as one continued Feast; but the remainder of the fifty days is also marked with special honors. To say nothing of the joy, which is the characteristic of this period of the year, and of which the Alleluia is the expression,- Christian tradition has assigned to Eastertide two practices, which distinguish it from every other Season.
The first is, that fasting is not permitted during the entire interval: it is an extension of the ancient precept of never fasting on a Sunday, and the whole of Eastertide is considered as one long Sunday. This practice, which would seem to have come down from the time of the Apostles, was accepted by the Religious Rules of both East and West, even by the severest.
The second consists in not kneeling at the Divine Office, from Easter to Pentecost. The Eastern Churches have faithfully kept up the practice, even to this day. It was observed for many ages by the Western Churches also; but now, it is little more than a remnant. The Latin Church has long since admitted genuflections in the Mass during Easter time. The few vestiges of the ancient discipline in this regard, which still exist, are not noticed by the faithful, inasmuch as they seldom assist at the Canonical Hours.
Eastertide, then, is like one continued Feast. It is the remark made by Tertullian, in the 3rd century. He is reproaching those Christians who regretted having renounced, by their Baptism, the festivities of the pagan year; and he thus addresses them: “If you love Feasts, you will find plenty among us Christians; not merely Feasts that last only for a day, but such as continue for several days together.
The Pagans keep each of their Feasts once in the year; but you have to keep each of yours many times over, for you have the eight days of its celebration. Put all the Feasts of the Gentiles together, and they do not amount to our fifty days of Pentecost.” [De Idolatria, cap. xiv.] St. Ambrose speaking on the same subject, says: “If the Jews are not satisfied with the Sabbath of each week, but keep also one which lasts a whole month, and another which lasts a whole year;- how much more ought not we to honor our Lord’s Resurrection? Hence our ancestors have taught us to celebrate the fifty days of Pentecost as a continuation of Easter. They are seven weeks, and the Feast of Pentecost commences the eighth. … During these fifty days, the Church observes no fast, as neither does she on any Sunday, for it is the day on which our Lord rose: and all these fifty days are like so many Sundays.” [In Lucam, lib. viii. cap. xxv.]