Why do we genuflect on entering a Catholic church? Because the Lord is present in the tabernacle. And we know that because the Lord is present in the Eucharist and the extra consecrated hosts are in a ciborium, locked in the tabernacle. But how do we know that?
Blessed Jacinta of Fatima, who was denied Holy Communion in this life, used to call the Eucharist “the Hidden Jesus”. Indeed, he is hidden beneath a facade of wheat. But she truly knew that the tabernacle housed Someone she loved and looked forward to receiving. She would watch the tabernacle from the balcony of the chapel where she stayed as she was dying. All Jacinta could do was adore.
The Church has taught officially about the Real Presence since the time of Ignatius of Antioch (105): “They stay away from the Eucharist and from prayer because they do not confess that the Eucharist is the flesh of our Redeemer, Jesus Christ, Who suffered from our sin, and Whom the Father, in His goodness, raised from the dead.”…”Be thee resolved, to celebrate one Eucharist only.” Throughout the early history of the Church, the Fathers of the Church reiterated St Ignatius’ words, declaring that the Host was more than a review of the Last Supper.
In the 800s, a priest who had doubts about the Real Presence saw his host change at the Consecration. It can be seen to this day, encased ina gold monstrance, in Lanciano, Italy, half wheat and half cardiac muscle. In 1996, in Buenos Aires, Argentina, an elderly Eucharistic minister dropped a host by accident and within a week, after sitting in water, it had developed spots of cardiac muscle. Samples of these two tissues were analyzed and found to be from the same man who had been badly injured. The unknown man was found to have a blood type of AB positive. Furthermore, the blood type matched that found on the Shroud of Turin.  Should you not believe that the blood types match, you should know that the real miracle may lie in the fact that the tissues could be typed at all, since most blood tissue degenerates within an hour of being taken from the body if not refrigerated.
So the Presence in the tabernacle is the true Jesus. This is the actual Jesus, the Son of the Father, the Creator. As the second Person of the Blessed Trinity, in union  with the Father, the Presence in the tabernacle is the Creator. The Creator of the world! The Creator of you!
If you have ever been lucky enough to be in the presence of the president of this country, or a king or queen, you know that you must practice exact protocol. You politely wait in line to shake the hand of the president. Or you curtsey, or bow, when presented to the royalty. Giving either the president or the queen of England a hug would probably get you thrown out of the place.
Our Lord, Jesus Christ,  is the royalty par excellence