So Jesus said to them, “Truly, truly, I say to you, unless you eat the flesh of the Son of Man and drink His blood, you have no life in yourselves. He who eats My flesh and drinks My blood has eternal life, and I will raise him up on the last day. For My flesh is true food, and My blood is true drink. He who eats My flesh and drinks My blood abides in Me, and I in him. As the living Father sent Me, and I live because of the Father, so he who eats Me, he also will live because of Me. This is the bread which came down out of heaven; not as the fathers ate and died; he who eats this bread will live forever.” These things He said in the synagogue as He taught in Capernaum. (6:53–59)
Although confronted with their willful unbelief, Jesus did not tone down, soften, or even clarify His words. Instead, He made His teaching even harder for them to swallow by adding the shocking concept of drinking His blood. To drink blood or eat meat with the blood still in it was strictly prohibited by the Old Testament law:
And any man from the house of Israel, or from the aliens who sojourn among them, who eats any blood, I will set My face against that person who eats blood and will cut him off from among his people. For the life of the flesh is in the blood, and I have given it to you on the altar to make atonement for your souls; for it is the blood by reason of the life that makes atonement. Therefore I said to the sons of Israel, “No person among you may eat blood, nor may any alien who sojourns among you eat blood.” So when any man from the sons of Israel, or from the aliens who sojourn among them, in hunting catches a beast or a bird which may be eaten, he shall pour out its blood and cover it with earth. For as for the life of all flesh, its blood is identified with its life. Therefore I said to the sons of Israel, “You are not to eat the blood of any flesh, for the life of all flesh is its blood; whoever eats it shall be cut off.” (Lev. 17:10–14; cf. 7:26–27; Gen. 9:4; Deut. 12:16, 23–24; 15:23; Acts 15:29)
Jesus, of course, was not speaking of literally drinking the fluid in His veins any more than He was of literally eating His flesh. Both metaphors refer to the necessity of accepting Jesus’ sacrificial death. The New Testament frequently uses the term blood as a graphic metonym speaking of Christ’s death on the cross as the final sacrifice for sin (Matt. 26:28; Acts 20:28; Rom. 3:25; 5:9; 1 Cor. 11:25; Eph. 1:7; 2:13; Col. 1:20; Heb. 9:12, 14; 10:19, 29; 13:12; 1 Peter 1:2, 19; 1 John 1:7; Rev. 1:5; 5:9; 7:14; 12:11). His sacrifice was the one to which all of the Old Testament sacrifices pointed.
But the concept of a crucified Messiah was a major stumbling block for Israel. In response to the Lord’s declaration, “And I, if I am lifted up from the earth, will draw all men to Myself” (John 12:32), “the crowd then answered Him, ‘We have heard out of the Law that the Christ is to remain forever; and how can You say, “The Son of Man must be lifted up?” ’ ” (v. 34). On the road to Emmaus, the resurrected Christ rebuked two of His disciples for their hesitancy to accept the necessity of His death: “O foolish men and slow of heart to believe in all that the prophets have spoken! Was it not necessary for the Christ to suffer these things and to enter into His glory?” (Luke 24:25–26). “We preach Christ crucified,” the apostle Paul wrote to the Corinthians, “to Jews a stumbling block” (1 Cor. 1:23), and in Galatians 5:11 he referred to the “the stumbling block of the cross.” Thus, the major thrust of Paul’s evangelistic message to the Jews at Thessalonica involved “explaining and giving evidence that the Christ had to suffer and rise again from the dead, and saying, ‘This Jesus whom I am proclaiming to you is the Christ’ ” (Acts 17:3).
It should be noted that the verbs translated eat and drink are aorists, not present tense verbs. That suggests a one-time appropriation of Christ at salvation, not the continual eating and drinking of His body and blood portrayed by the Roman Catholic Mass (see the discussion of v. 52 above).
In verses 53–56 Jesus made four promises to those who eat His flesh and drink His blood. The first one is expressed negatively; those who reject Jesus have no life in themselves. Conversely, then, those who appropriate Him by faith do have such life. They are guaranteed abundant spiritual life, even now, by the Lord Himself (5:24; 10:10).
The second promise is that the one who eats His flesh and drinks His blood has eternal life. The abundant life that believers experience in the present will not end with death, but will expand into completeness and last forever. That this verse does not describe a ritualistic act is obvious when it is compared with verse 40. The results in the two verses are the same: eternal life and resurrection. But in verse 40, those results come from beholding and believing in the Son, while in verse 54 they come from eating His flesh and drinking His blood. It follows, then, that the eating and drinking of verse 54 are parallel to the beholding and believing of verse 40.
The third promise, that Christ will raise up on the last day all who eat His flesh and drink His blood, is repeated here for the fourth time in this passage (vv. 39, 40, 44). The resurrection to everlasting life is the believer’s great hope (Acts 23:6; 24:15; cf. Titus 2:13; 1 Peter 1:3); apart from it, the Christian gospel is meaningless. To the Corinthians, some of whom were questioning the reality of the resurrection, Paul wrote,
Now if Christ is preached, that He has been raised from the dead, how do some among you say that there is no resurrection of the dead? But if there is no resurrection of the dead, not even Christ has been raised; and if Christ has not been raised, then our preaching is vain, your faith also is vain. Moreover we are even found to be false witnesses of God, because we testified against God that He raised Christ, whom He did not raise, if in fact the dead are not raised. For if the dead are not raised, not even Christ has been raised; and if Christ has not been raised, your faith is worthless; you are still in your sins. Then those also who have fallen asleep in Christ have perished. If we have hoped in Christ in this life only, we are of all men most to be pitied. (1 Cor. 15:12–19)
Jesus introduced the fourth and final promise by declaring that His flesh is true food, and His blood is true drink—the sustenance that provides the very life of God to the believer. In light of that, the Lord declared, “He who eats My flesh and drinks My blood abides in Me, and I in him.” The promise here is that of union with Christ. In John 14:20 Jesus promised His disciples, “In that day you will know that I am in My Father, and you in Me, and I in you.” In 15:5 the Lord declared, “I am the vine, you are the branches; he who abides in Me and I in him, he bears much fruit, for apart from Me you can do nothing.” “If anyone is in Christ,” Paul wrote, “he is a new creature; the old things passed away; behold, new things have come” (2 Cor. 5:17). Later in that same epistle the apostle exhorted the Corinthians, “Test yourselves to see if you are in the faith; examine yourselves! Or do you not recognize this about yourselves, that Jesus Christ is in you—unless indeed you fail the test?” (2 Cor. 13:5). To the Galatians he wrote, “I have been crucified with Christ; and it is no longer I who live, but Christ lives in me; and the life which I now live in the flesh I live by faith in the Son of God, who loved me and gave Himself up for me” (Gal. 2:20). “Christ in you,” he reminded the Colossians, is “the hope of glory” (Col. 1:27). In his first epistle the apostle John wrote, “We know that the Son of God has come, and has given us understanding so that we may know Him who is true; and we are in Him who is true, in His Son Jesus Christ. This is the true God and eternal life” (1 John 5:20; cf. 2:24; 3:24; 4:13; John 17:21; Rom. 6:3–8; 8:10; 1 Cor. 1:30; 6:17; Eph. 3:17; Col. 2:10).
In verse 57 Jesus declared the source of His authority to make such promises: “the living Father sent Me, and I live because of the Father, so he who eats Me, he also will live because of Me.” Jesus had earlier stated, “As the Father has life in Himself, even so He gave to the Son also to have life in Himself” (5:26). Therefore, those who believe in Jesus will live because of Him. Jesus has life in Himself; and believers also have life in Him.
The Lord concluded this magnificent teaching by repeating the thought of verses 49 and 50. The invitation is as clear today as it was that memorable day in the synagogue … in Capernaum. The one who pursues material things will die as surely as the rebellious Israelites died in the wilderness. But he who eats the bread which came down out of heaven … will live forever.
https://www.gty.org/library/bibleqnas-library/QA0260/communion-and-the-body-of-christ