We worship and serve Christ, who is the Incarnation of the God of all grace. We come to partake of Him here, and this means that we come to be partakers of His grace.
Now this table is all grace. The cup is a cup of blessing, and the bread is the bread of life. But this creates a question. How can a table of blessing bring destruction? Why had some of the Corinthians died as a result of their sacrilegious approach to the Table?
When grace is despised, it does not cease to be objectively grace, but it does cease to be experienced as grace by the one who despises it. When someone approaches God in unbelief, his unbelief is superficially confirmed to him—what he does not believe the sacrament to be (the blessing of God) is confirmed in his experience. He does not believe it to be the goodness of God, and for him, it is not. This does not justify his unbelief, for the gracious nature of the sacrament remains.
For those who come in faith, the reverse is true. In his Institutes, John Calvin points out that sacraments effect the blessings they signify, but they only do this for those who come to them in genuine faith. If you chew the sacrament with your teeth only, then you are not partaking of the blessing. You must chew and swallow Christ in Your hearts. You don’t do this by any means other than what God has set forth in His Word—simple, unadulterated faith.