"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'" (Jn.6:53). Many who were initially His disciples left Him when they heard this because they got offended with this (v.66). Even now many don't understand this. Some wrongly think that this refers to the communion where they eat the bread and drink the wine. But what we eat and drink or do physically cannot give us the eternal life that Jesus gives. The bread and wine are for us to remember what Jesus has done for us (1Co.11:24-26) so that we can examine our life and rededicate ourselves to Him. They do not give us life in a mystical kind of way.
What does it mean to drink His blood? In simple terms it means that we recognise, acknowledge and accept for ourselves what it does for us. His blood was the sign of the new covenant because of which there is forgiveness for our sins (Mt.26:28). There is no forgiveness in any other way or in any other name. To receive this – drink it – we need to recognise we are sinners in God's eyes, admit it to Him, turn away from sin and receive forgiveness as a free gift from Him. Jesus shed His blood for the forgiveness of the whole world (1Jn.2:2), but we are not forgiven until we come to Him in faith like this.
Jesus broke the bread and gave His disciples saying it represented His body. His body was broken on the cross for the bearing of our sins. There was also another way in which His body (flesh) was broken for us. That was when every day of His life He (virtually) carried His cross, denied His will when He was tempted (He.4:15) and did the Father's will. When we have come to be forgiven and accepted as children of God through the blood of Jesus Christ, don't we also need to walk in His ways in this manner (1Jn.2:6)? It is when we do this that we actually partake of His divine nature.
What if we come to God through the blood of Christ, know that we have eternal life, and then live our own life, doing whatever we like, pleasing ourselves? That is when we treat the blood of Christ which was shed for us at great cost as if it was dirt cheap! Then we imagine that we are 'free from the law' and we can do anything because the blood of Christ will forgive us!
But it is those who eat His flesh and drink His blood who have eternal life. I am not saying we have to earn this life. No, we receive it by grace through faith (Ep.2:8,9). But when we have been given access to God by this grace (v.18), don't we need to make use of that access and learn to live a life that is pleasing to Him? Only then can we be obedient to Him (1Jn.2:3,4), do His will instead of ours (Lk.22:42) and bring great delight to His heart and honour to His name (Jn.15:8). We may think this is hard on our flesh, but that is what will get us closer to Him, enhance our fellowship with Him and make our life meaningful and fulfilling (Jn.14:23). Then our heart will be set on Him.