Why do we celebrate Holy Communion? First, because our Lord and Saviour has instructed us to do so which is why we also call it the Lord's Supper and within the Church of England have historically celebrated it in close accordance with Christ's instructions rather than allowing for the withdrawal of one of the elements (as in the Roman Catholic church) or mixing the elements (as in the Orthodox churches).
But is it not pure and blind obedience that motivates us. We expect to benefit from partaking in Holy Communion. What is the benefit that Holy Communion conveys? It is of course Jesus Christ. There is nothing of substance offered to us in Holy Communion that is not offered to us by other means of grace as well.
Both Word and Sacrament offer us the same: Jesus Christ. Why, then, do we not confine ourselves to Services of the Word during a pandemic?
But if a man, either by reason of extremity of sickness, or for want of warning in due time to the Curate, or for lack of company to receive with him, or by any other just impediment, do not receive the Sacrament of Christ's Body and Blood: the Curate shall instruct him that if he do truly repent him of his sins, and stedfastly believe that Jesus Christ hath suffered death upon the Cross for him, and shed his Blood for his redemption, earnestly remembering the benefits he hath thereby, and giving him hearty thanks therefore; he doth eat and drink the Body and Blood of our Saviour Christ profitably to his soul's health, although he do not receive the Sacrament with his mouth.
These words are from the Book of Common Prayer (1662) order of service for the Communion of the Sick which make it plain that the spiritual benefits conveyed by receiving the Sacrament can also be received without receiving the Sacrament. But in the same place the importance of receiving the Sacrament is stressed:
the Curates shall diligently from time to time (but especially in the time of pestilence, or other infectious sickness) exhort their Parishioners to the often receiving of the holy Communion of the Body and Blood of our Saviour Christ, when it shall be publicly administered in the Church; that so doing, they may, in case of sudden visitation, have the less cause to be disquieted for lack of the same.
The rubric links such reception with readiness to die and suggests that notwithstanding the fact that nothing is offered in Holy Communion that is substantially different from what we can receive without the Sacrament, there is nevertheless benefit to be had from partaking of Holy Communion.
How might we go about defining this benefit? If the Sacrament offers us nothing different from the faithful preaching of God's Word, it nevertheless offers us the same Jesus Christ differently. And this is perhaps where one of the great Reformation disagreements kicks in. While some might say that Christ is offered to us in a different form (materially rather than spiritually), others might say that Christ is offered to us in a different manner (by eating and drinking rather than hearing).
Such and other fundamental disagreements seem to lie behind the current controversy within the Church of England on the mode of administration of Holy Communion during a pandemic.
Some, stressing that the physical reception of Holy Communion does not offer us anything different from what can be received without Holy Communion, were content to suspend services of Holy Communion altogether for a while.
Others, focusing on the (alleged) benefits of the Sacrament for parties who do not partake of it in analogy to verbal intercessory prayer, were content to celebrate the Eucharist without a congregation.
Those who believe that Christ is offered in a different form in the Sacrament were keen to offer Holy Communion to the people but where the doctrine of concomitance was added to (something like) a doctrine of transubstantiation, priests were content to deny the cup to the laity on the grounds that it offers nothing in addition to what is offered in the bread. It is in effect superfluous, at least as far as the consumption by the people is concerned (consecration and consumption by one is still necessary, even if its benefit cannot be explained).
Those who believe that Christ is offered to us in a different manner in the Sacrament are not happy to have this impaired by a mode of administration which compromises the instructions of our Lord and Saviour to eat and drink and point out that in the Book of Common Prayer instructions for the administration of Holy Communion both kinds are to be separately offered into the hands of the people.
If we do not receive a different matter / substance in Holy Communion, the benefits of the Sacrament must lie in the different experience which is why we should ensure that all the faithful are offered the experience of eating from the one bread and drinking from the one cup.
See also my posts on Celebrating Holy Communion, Receiving Holy Communion.and The Distribution of the Elements among others or search for the label Holy Communion.