The Promise of Christ's Word in the Lord's Supper...

Consider this true, almighty Lord, our Creator and Redeemer, Jesus Christ, after the Last Supper. He is just beginning His bitter suffering and death for our sins. In those sad last moments, with great consideration and solemnity, He institutes this most venerable Sacrament. It was to be used until the end of the world with great reverence and obedience. It was to be an abiding memorial of His bitter suffering and death and all His benefits. It was a sealing of the new Testament, a consolation of all distressed hearts, and a firm bond of unity for Christians with Christ, their Head, and with one another. In ordaining and instituting the Holy Supper, He spoke these words about the bread, which He blessed and gave: "Take, eat; this is My body, which is given for you," and about the cup or wine: "This is My blood of the new testament, which is shed for you for the forgiveness of sins."

We, too, are simply to believe with all humility and obedience our Creator and Redeemer's plain, firm, clear, solemn words and command, without any doubt and dispute about how it agrees with our reason or it is possible. For these words were spokne by that Lord who is infinite Wisdom and Truth itself. He can do and accomplish everything He promises.
~BOC, FSD, VII, 44,47