John 6:41-42 "The Jews began to grumble about Him (Jesus) saying He was the Bread of Life."
John 6:43-48 "Jesus answered, 'Stop your grumbling among yourselves. No one can come to Me unless the Father Who sent Me draws him and I will raise him up at the last day (The Rapture). It is written in the Prophets, they will be taught by GOD. Everyone who listens to the Father and learns from Him comes to Me. No one has seen the Father except Him Who comes from the Father, only He has seen the Father (that is Jesus.) I tell you the truth, he who believes has everlasting life. I AM the Bread of Life...I AM the Living Bread of Life that came down from heaven. Anyone who eats of this bread will live forever." To eat living bread means to accept Christ Jesus into our lives and become united with Him (through the entering of the Holy Spirit.) We are united in Christ in two ways: 1. by believing in His death (the sacrifice of His flesh and shedding of His blood for our sins) and resurrection and 2. by devoting ourselves to living as He requires, depending on His teaching for guidance, and trusting in the Holy Spirit for power. The apostle Paul uses the imagery of flesh and blood in taking communion (I Corinthians 11:23-26) (Bible commentary)
Jesus Christ alone is the only acceptable sacrifice for mankind, because He is Almighty GOD in the flesh. Mankind is fallen and there is no "good" that any man/woman can do in and of himself/herself to make up for it. "All man's righteousness is as filthy rags before Holy GOD." (Isaiah 64:6) "There is no (man) righteous, no not one." (Romans 3:10) Only by believing what Jesus did for us on the Cross will take away every sin. There is no other way but the Way of the Cross. "He (she) who has ears, let him/her hear what the Spirit says to the churches." (Revelation 2:7)