This is a wonderful verse. It is obviously metaphorical.
Obviously, the passage from John that Dr. Kopp quoted showed that the Jews to whom he was speaking, and some of his disciples, were stunned by his words and
60 Many of his disciples, when they heard it, said, "This is a hard saying; who can listen to it?"61 But Jesus, knowing in himself that his disciples murmured at it, said to them, "Do you take offense at this?
62 Then what if you were to see the Son of man ascending where he was before?
63 It is the spirit that gives life, the flesh is of no avail; the words that I have spoken to you are spirit and life.
64 But there are some of you that do not believe." For Jesus knew from the first who those were that did not believe, and who it was that would betray him.
So, basically, many disciples didn't believe Jesus' words but he didn't clarify his meaning by saying, "I meant this as a blessing" or "this is a symbol of my body" but instead reiterated His words, and many disciples left, not being about to accept His words.
To me, the Holy Eucharist is the most important and explicit and obvious Sacrament handed down from God after Baptism. Through Baptism, we die with Jesus so that we may share eternal life with Him. Through the Holy Eucharist, we share Jesus' life weekly or daily to bring us closer to Him.
God bless.