While there are various reasons that led to my conversion, the ultimate reason is the Eucharist. If the Eucharist is real, then I knew I had to be Catholic, and if it wasn't, then I shouldn't be. At one point before my conversion, I tried to convince myself that the Eucharist couldn't possibly be the Body and Blood of Jesus because consuming blood had been forbidden, and surely Jesus wouldn't reverse that (let's forget the fact that I ate my steak medium rare, and certainly didn't get meat from kosher butchers). What I neglected to consider, though, was why consuming blood was forbidden. (all Scripture references are from the New Jerusalem Bible)
Genesis 9:4 "you must not eat flesh with life, that is to say blood, in it"
Leviticus 17:11 "For the life of the creature is in the blood, and I have given it to you for performing the rite of expiation on the altar for your lives, for blood is what expiates for a life."
So consuming blood was forbidden because the life was in the blood, and because blood was what expiated for life. So what does Jesus say? Let's look at John 6. The beginning of the chapter is about the multiplication of the loaves and fishes, and then the crowds follow Him, and He says (v27) "27 Do not work for food that goes bad, but work for food that endures for eternal life, which the Son of man will give you, for on him the Father, God himself, has set his seal." Then He goes on to elaborate:
|48 I am the bread of life.|
|49 Your fathers ate manna in the desert and they are dead;|
|50 but this is the bread which comes down from heaven, so that a person may eat it and not die.|
|51 I am the living bread which has come down from heaven. Anyone who eats this bread will live for ever; and the bread that I shall give is my flesh, for the life of the world.'|
|52 Then the Jews started arguing among themselves, 'How can this man give us his flesh to eat?'|
|53 Jesus replied to them: In all truth I tell you, if you do not eat the flesh of the Son of man and drink his blood, you have no life in you.|
|54 Anyone who does eat my flesh and drink my blood has eternal life, and I shall raise that person up on the last day.|
|55 For my flesh is real food and my blood is real drink.|
|56 Whoever eats my flesh and drinks my blood lives in me and I live in that person.|
|57 As the living Father sent me and I draw life from the Father, so whoever eats me will also draw life from me.|
|58 This is the bread which has come down from heaven; it is not like the bread our ancestors ate: they are dead, but anyone who eats this bread will live for ever.|
So what did the early Christians think? Here's a quote from St Ignatius of Antioch, a disciple of St John the Apostle: "They abstain from the Eucharist and from prayer, because they confess not the Eucharist to be the flesh of our Saviour Jesus Christ, which suffered for our sins, and which the Father, of His goodness, raised up again." Ignatius of Antioch, Epistle to Smyrnaeans, 7,1 (c. A.D. 110)
And a quote from St Justin Martyr: "For not as common bread and common drink do we receive these; but in like manner as Jesus Christ our Saviour, having been made flesh and blood for our salvation, so likewise have we been taught that the food which is blessed by the prayer of His word, and from which our blood and flesh by transmutation are nourished, is the flesh and blood of that Jesus who was made flesh." Justin Martyr, First Apology, 66 (c. A.D. 110-165).
(quotes were found on Scripture Catholic)
My belief has only been confirmed and strengthened by looking at various Eucharistic miracles, my favourite being the miracle at Lanciano.