As I see it, there are two major exegetical/preaching challenges in this text. The first major issue we face in this text is what Jesus meant here when he said he was the bread of life and spoke of eating his flesh and drinking his blood. The second issue is his challenging questions to the disciples, ”Do you take offense at this?…Do you want to go away as well?”
On the first issue, I can remember a time when I thought my teachers – those in the classroom, those in Bible studies, and those I read in books – were often too timid about connecting Jesus’ teaching in this chapter with the Lord’s Supper. I saw the similar elements involved and thought, “Come on…be bolder about using this passage to teach the wonder of the Lutheran understanding of the Supper.” Over the years though I have come to be just as cautious as my teachers were.
Professor Buls gives thorough reasoning for caution on this matter:
a. The eating which Jesus speaks of in verse 53 is absolutely necessary for salvation. Even Old Testament believers did this by faith in the promises. But Old Testament believers did not partake of the Lord’s Supper.
b. The eating and drinking spoken of here in verse 54 is always salutary. But the Sacrament can be eaten to one’s temporal and eternal condemnation.
c. The audience in John 6 is totally different from that of the Lord’s Supper. Jesus is trying to convert unbelievers here.
d. Jesus uses “flesh” not “body”. Read verses 47-50 in one sweep. The words “eat” and “drink” are used figuratively for “believe.” The word “bread” is also used figuratively for that which not only sustains life but also gives life. Ordinary bread cannot do that.
e. To make Jesus say in verse 63: “MY flesh helps nothing” makes Jesus contradict Himself.
f. In the words of institution of the Lord’s Supper the words “eat, drink, body, blood” are not qualified. There is nothing in that context to indicate that these words are to be taken figuratively.
g. John 6 took place a year before the Lord’s Supper was instituted.
h. In John 6 Jesus is speaking about justification through faith and the universal atonement. (http://pericope.org/buls-notes/john/john_6_51_58.htm)
As to the second issue, this text is a clear opportunity to discuss the various crucial crossroads we face in life. Perhaps the secular wisdom of Robert Frost’s poem, The Road Not Taken, would be a good segue into this aspect of the text.
The challenge for the preacher is to talk about those crossroads in a way that both recognizes the reality of those calls to live by faith in our lives and also admits the horrible limitations placed on us by our old nature. The faithful exegete cannot simply say, don’t you see it? Now make the right choice. That would ignore the awful reality of the old man that Romans 3 speaks so clearly about.
Jesus deals with that issue even as he challenges the disciples with his questions. “It is the Spirit who gives life, the flesh is no help at all.” (v. 63)
Jesus says calm down…set aside your pride and listen to me. I know your old nature and its tendencies. I tell you this not to embarrass you and make you feel insignificant and powerless, but I tell you this to encourage you. The Spirit gives life…and the Father is the one who enables our choices. These truths remind us that we are not alone in making the important choices of life. The Father is the one who enables us. Don’t just think of this truth negatively…as it says in the explanation to the third article: “I believe that I cannot by my own reason or strength believe in Jesus Christ my Lord or come to him.” That is such a humbling realization. But never stop at this point. Luther goes on to say, “but the Holy Spirit has called me through the Gospel, enlightened me with his gifts, and sanctified and preserved me in the true faith…” The wonderful reality is that the Father does indeed enable us in all of the choices we face if we but give him the opportunity. The bad choices we make are those we make on our own. But as we look to our Lord in faith he will lead us through all of life’s choices. He will enable us to make the right choice. Sometimes we might not even be aware of what the right choice is as we follow by faith. Remember, the word tells us that we walk by faith and not by sight. To make a choice by faith by definition means that you will not always understand. And yes, sometimes our ideas will override what God is trying to say to us, but as long as we trust in him, we can know that he will never grow tired of enabling us to find him and his will for us. Never cut yourself off from that enabling of the Father through His Spirit. Always dig into His word that your choices may be enlightened by his written will. Trust him and he will never fail you, no matter how difficult the circumstances of life and the choices those circumstances will require of you.
Tie those two issues (“I am the bread of life” and “Do you want to go away as well?”) together with the thought that it is “the Spirit who gives life” and you have a powerful sermon.