J.M..J.
In 700 A.D., a priest, doubting in the Real Presence was saying Mass. After the words of consecration, the bread visibly changed into Flesh, and the wine into Blood.
In the 13th century, another priest, also doubting the Real Presence, witnessed blood dripping from the Host, staining the corporeal, as he barely said the words of consecration. Pope Urban IV investigated this miracle and, in honour of it, established a new feast: Corpus Christi.
These are just two of many Eucharistic miracles which have occurred throughout history - all of which are testament to the Real Presence of Christ Jesus in the Most Holy Sacrament of the Altar. Some say this miracle is the greatest, others claim another. In my opinion, this is the greatest Eucharistic miracle:
The Transubstantiation.
Yes, the miracle that is, was, and shall be repeated at every Mass is my favourite of all Eucharistic miracles. Mere bread and wine, by the power of the Holy Spirit, transform into the true Body and true Blood of our Lord, Jesus Christ.
Is that not plain usual and boring?
Well, the Transubstantiation is the most important miracle because it is indispensable, and is the most amazing simply because it happens at every single Mass. It is the miracle that fulfils Christ's motivation behind instituting the Holy Eucharist - to feed His flock. Jesus Himself said, "Whoever eats my flesh and drinks my blood remains in me and I in him." (Jn 6:56) So infinite is this miracle and the grace that flows from it!
Imagine what would happen if the Gifts ceased to turn into the Body and Blood of our Saviour. All the faithful will be denied of the graces promised in this great Sacrament. In addition, Pope Emeritus Benedict XVI says, "Without the Eucharist, the Church simply does not exist." And if the Transubstantiation does not occur, we worship bread, and will be idolators. I believe most of us would condemn ourselves to Hell over such a grievous sin.
All the other miracles add to the faith of those who choose to believe them, yet many still persist in disbelief and find ways and means to offer alternative explanations behind these miracles. If they never happened, those strong in faith will still confess in the Real Presence. Therefore, these miracles only confirm, for the doubters, what is already true: that Transubstantiation occurs. Yes, these miracles are great, deserve to be proclaimed, and are useful in evangelisation. We should praise God for them. But they are still dispensable.
Therefore, I urge you to, at subsequent Masses, recall the moment of consecration, where Transubstantiation occurs, as the greatest Eucharistic miracle. As the priest elevates the Host, adore Him with intense love, and as the priest genuflects, bow your head in deep thanksgiving for that wonderful miracle.
Verbum caro, panem verum
Verbo carnem efficit:
Fitque sanguis Christi merum,
Et si sensus deficit,
Ad firmandum cor sincerum
Sola fides sufficit.
(Pange Lingua Gloriosi Verse 4 - St Thomas Aquinas)