John 6:56 He that eateth my flesh, and drinketh my blood, dwelleth in me, and I in him.
Eating this flesh and drinking this blood mean believing in Christ.
John 6:63 It is the spirit that quickeneth; the flesh profiteth nothing: the words that I speak unto you, they are spirit, and they are life.
His teaching is to be, not carnally, but spiritually understood. They think of a physical eating of His flesh, and this offends them;
It is not therefore the carnal eating of my flesh that I intended, that is a very gross conception of yours;
nor can any such thing as that do you good:
but the words that I speak to you, they are spiritual, and such by the belief of which you may obtain a spiritual and eternal life;
for by believing those words, and obeying them, you shall come to believe in me, which is that eating my flesh and drinking my blood which I intended, not any corporeal or carnal eating.
the flesh profiteth nothing—Much of His discourse was about “flesh”; but flesh as such, mere flesh, could profit nothing, much less impart that life which the Holy Spirit alone communicates to the soul.
John 7:38-39 He that believeth on me, as the scripture hath said, out of his belly shall flow rivers of living water. (But this spake he of the Spirit, which they that believe on him should receive: for the Holy Ghost was not yet given; because that Jesus was not yet glorified.)
Matthew 15:17 Do not ye yet understand, that whatsoever entereth in at the mouth goeth into the belly, and is cast out into the draught?
Acts 7:48-50 Howbeit the most High dwelleth not in temples made with hands; as saith the prophet, Heaven is my throne, and earth is my footstool: what house will ye build me? saith the Lord: or what is the place of my rest? Hath not my hand made all these things?
The martyrs spoke against the false Roman Catholic doctrine of Transubstantiation. Many were martyred for their faithfulness in defending the truth of God’s Word.