A bicycle is a pretty simple machine, but I doubt you understand the science behind how a bike works. I certainly don’t. According to interestingengineering.com, several theories about how bikes remain stable have been disproven (the gyroscopic theory and the caster theory).  A bike is a simple machine, and yet, the exact mechanism that makes a bicycle stable is a mystery.
Okay, if a simple machine involves mysteries that scientists can’t figure out or explain, how much more are the Lord’s Supper and the operation of the Holy Spirit through the Word and sacraments? Who can fathom the mechanism of God’s grace?
Jesus said, “Take, eat; this is my body” (Matt. 26:26). Jesus said, “This cup that is poured out for you is the new covenant in my blood” (Lk. 22:20). Paul explained that the cup of wine and the bread are “a participation in the blood [and body] of Christ” (1 Cor. 10:16-17). What do these mysteries mean? And how does the Holy Spirit use the Lord’s Supper for our spiritual benefit? Consider Jesus when he said, “The wind blows where it wishes, and you hear its sound, but you do not know where it comes from or where it goes. So it is with everyone who is born of the Spirit” (Jn. 3:8). So the wind is a mystery as is the work of the Holy Spirit.
Many Christians think of the Lord’s Supper as a mere memorial. If that’s all the Supper is, a mere memorial, then it’s empty of divine grace and blessing, and the Holy Spirit is doing nothing for us as we eat and drink. That seems very unlikely and very incongruent with the words of Jesus and Paul.
Article 35 of the Belgic Confession talks about the mysteries of the Supper:
Now it is certain that Jesus Christ did not prescribe his sacraments for us in vain, since he works in us all he represents by these holy signs, although the manner in which he does it goes beyond our understanding and is incomprehensible to us, just as the operation of God’s Spirit is hidden and incomprehensible. Yet we do not go wrong when we say that what is eaten is Christ’s own natural body and what is drunk is his own blood—but the manner in which we eat it is not by the mouth but by the Spirit, through faith. 
Do you believe that you are doing something for Christ in the Supper or that Christ is doing something for you? Is the Supper law or gospel? The Belgic is clear. The Lord’s Supper is not a vain sacrament, meaning it’s not empty of grace. It is not a pretend meal. It is a true meal for the soul. As we eat by faith, Christ works in us all that the bread and wine signify and seal. Christ feeds us the benefits of the gospel. How does he do it? Well, that’s a mystery. The Belgic says, “it goes beyond our understanding and is incomprehensible to us.”
Is it mysterious to say we eat “Christ’s own natural body” and drink “his own blood”? Yes. However, we must understand that we do not eat and drink Christ with the mouth; we eat and drink Christ by the Spirit through faith. The Holy Spirit gives us Christ in the Lord’s Supper for the nourishment and refreshment of our souls. This is entirely consistent with the language of Jesus and Paul and the character of our Savior.
What do you eat in the Supper? Well, that question could do in one of two directions. What do you eat with your mouth in the Supper? Easy. Bread and wine. You do not eat the physical flesh and blood of Christ with your mouth. That would be cannibalism and creepy. You eat bread and wine. But, there’s another kind of eating. Right? Absolutely. Consider John 6. And what did Jesus mean by telling Peter, “Feed my lambs. . . . Feed my sheep” (Jn. 21:15, 17)? This kind of eating is eating with the soul. What do you eat with your soul in the Supper? You eat the true body and true blood of Christ spiritually as the Holy Spirit graciously feeds you. Christ himself is given to you in the Supper to eat so that your faith is strengthened and your soul nourished and refreshed. That makes sense. There’s a parallel between physically eating and drinking and spiritually eating and drinking.
This is what Heidelberg 75 explains. I recommend that you read that now. It’s a very helpful statement. See, God appeals to our senses. As we hear the minister explain the gospel as he serves the Supper, God gives us something to look at. Not stained glass. Not a TV show. Bread and wine. Bread and wine (and the water of baptism) are the divinely sanctioned images of Christ and the gospel given for our spiritual growth and comfort. We smell the bread and wine. We touch the bread and wine. We taste the bread and wine. All the while, the Holy Spirit is working through the gospel to bolster our faith. As we believe the gospel, we are partaking of Christ’s crucified body and shed blood and receiving all the benefits of the gospel including the forgiveness of sins. The bread and wine have no inherent power or effect. Yet, the Holy Spirit works in and through the Supper to build our faith and apply the benefits of the gospel to us for our nourishment, assurance, and comfort.
Where is Christ? Christ is bodily at the right hand of God in heaven. He is not on earth. So, how does he commune with us in the Supper? Article 35 continues:
In that way Jesus Christ remains always seated at the right hand of God the Father in heaven—but he never refrains on that account to communicate himself to us through faith. This banquet is a spiritual table at which Christ communicates himself to us with all his benefits. At that table he makes us enjoy himself as much as the merits of his suffering and death, as he nourishes, strengthens, and comforts our poor, desolate souls by the eating of his flesh, and relieves and renews them by the drinking of his blood. 
Please, please, please don’t miss the comfort of the Reformed view of the Lord’s Supper. No other view is like it. This will comfort you many times over if you understand it. Jesus truly communes with you in the Supper. He gives you himself through faith for your spiritual benefit. The Supper is a means of his marvelous grace. The Supper is a spiritual banquet table to which you come to receive grace and soul-nourishment from Christ himself. Christ is the host, and you come to his table to be fed by him. He will give you grace as you come in faith. You are the one with the poor and desolate soul. You are the weak and weary. And when you come, your Lord, the one rich is grace, feeds you himself to the nourishment, strength, and comfort of your soul. You eat his flesh by faith. You drink his blood by faith. Jesus relieves and renews your soul with himself. This is so comforting and entirely consistent with the character and work of Christ. He is the vine; we are the branches. Right? He nourishes and sustains us with himself. Right? We can do nothing apart from his provision of grace. Right? The Bible answers, “Right! Right! Right!”
Take comfort, dear ones; Christ will nourish and sustain you by feeding you himself. Your Savior and Lord beckons: “Take, eat; this is my body. . . . Drink of it, all of you, for this is my blood.” Eat, drink, and persevere in godliness by the grace provided to you in the Supper.
Quotes from the Heidelberg Catechism are taken from Zacharias Ursinus & Jonathan Shirk, The Heidelberg Catechism (Manheim: Small Town Theologian, 2021).
Scripture quotations are from the ESV® Bible (The Holy Bible, English Standard Version®), copyright © 2001 by Crossway, a publishing ministry of Good News Publishers. Used by permission. All rights reserved. May not copy or download more than 500 consecutive verses of the ESV Bible or more than one half of any book of the ESV Bible.