In John 6, Jesus calls Himself the Bread of Life. Martin Luther comments:
“The whole chapter from which this Gospel is taken speaks of nothing but the spiritual food, namely, faith. It is now evident that whoever has faith in this bread of heaven–in Christ, in this flesh and blood, of which he here speaks that it is given to him and that it is his–he also accepts it as his own, and has already done the will of God and eaten of this heavenly manna.” (Martin Luther, On Faith And Coming To Christ, And the True Bread of Heaven)
Luther taught that eating of the Bread of Life means having faith in Jesus as our Savior. This faith is imparted to us regardless of our own merit or sinfulness as the manna was given to the Israelites in the wilderness. We exercise this gift of faith everytime we partake of Communion for we believe that we partake of His true Body and Blood Communion and so receive the mercy and grace He attained for us at cross.
Yet Jesus meant more than that when he referred to Himself as the Bread of Life which confused the Jews as much as it confuses many in our world today. This is because our culture values and emphasizes the sovereignty of the individual and on the freedom to choose. This contradicts what Jesus says because he means that it is impossible for man by his own efforts to achieve salvation. Salvation comes not by mere mental assent, or by agreeing that Jesus was a good man, a good moral teacher, perhaps one among many. Salvation comes not by religion or good works.
Salvation is by eating the Bread of Life, that is, by having faith is Jesus, by the bowing of the knee to accept our sinfulness and accept Him and the mercy, grace and eternal life earned by His work on the cross of Calvary. It is not just a matter of believing about Him, but of trusting in Him alone for eternal salvation. And mankind does not like that idea because man has no control over it nor does it boost his self-esteem or pride to realize that he is incapable of doing good. We all need faith in Jesus to enter into eternal life. We all need to say with Peter “Lord, to whom shall we go? You have the words of eternal life, and we have believed, and have come to know, that you are the Holy One of God.” (John 6:68-69, ESV)