If we want to understand the Lord’s Supper and the content of the communion cup, we must define our terms. What is the Lord’s Supper? How should we define it?

It’s harder to define the Lord’s Supper than we might think. That’s because the Bible–which is the only reliable source of information about the Lord’s Supper–does not contain a definition for the Lord’s Supper in the ordinary sense. This might surprise us, at first, but we should remember that the Bible is not a dictionary. If we look for simple definitions in it, we will be disappointed. Instead, the Bible helps us to arrive at definitions for words like “covenant” and “justification” by giving us the data we need to formulate the definitions of the terms we use. This data might be scattered throughout the Bible, but we can still find it, study it, and organize it.

In the case of the Lord’s Supper, we are especially blessed, because the great Westminster Assembly has already defined the Lord’s Supper for us. Westminster Shorter Catechism 96 asks, “What is the Lord’s Supper?” The answer is a very good definition for the Lord’s Supper:

“The Lord’s Supper is a sacrament, wherein, by giving and receiving bread and wine, according to Christ’s appointment, his death is showed forth; and the worthy receivers are, not after a corporal and carnal manner, but by faith, made partakers of his body and blood, with all his benefits, to their spiritual nourishment, and growth in grace.”

A great deal can be said, and should be said, about this definition for the Lord’s Supper, but for our purposes, only two things need to be observed. First, wine is an integral part of this definition. Wine must be given. Wine must be received. Second, unfermented grape juice is NOT a part of the definition for the Lord’s Supper.

The implications are obvious. Wine is an essential part of the Lords Supper. Wherever wine has not been given and received, the Lord’s Supper has not been observed. This is true even if grape juice is used in the place of the missing wine.

An illustration may help us to understand this point.

A triangle can be defined as a geometric figure with three sides. If a geometric figure has four sides, or if one of the three sides of a triangle suddenly disappears or is erased, or if a side is replaced with a circle, it is not a triangle. It no longer meets the definition for “triangle.”

In the same way, the Lord’s Supper is defined as a sacrament that uses bread and wine. If one of these elements is suddenly taken away, it is not the Lord’s Supper, even if the missing element is replaced with something else. It no longer meets the definition for the Lord’s Supper; therefore, it is not the Lord’s Supper.

If this analysis is correct, it refutes several popular notions about the use of grape juice. Some people have suggested that a Lord’s Supper that uses grape juice is just as valid as one that uses wine. They say grape juice is close enough to wine. Others have said that, though wine is to be preferred, grape juice, while less than perfect, is a legitimate substitute; therefore, the question of whether to use wine or grape juice is not urgent, and need not much concern us. “Why trouble the church over such trivial matters, when our custom of using grape juice so closely resembles the example of Jesus?”

However, as we have seen, the truth is very different. The truth of God’s word regarding the holy sacrament cannot be a trivial matter. That word must determine both our doctrine and our practice. What does the Bible say?

Has the word of God given us the authority to alter the Bible’s definition of the Lord’s Supper? Has it given us the right to regard wine as less than essential to the sacrament? Is a Lord’s Supper that uses grape juice still the Lord’s Supper? If we answer these questions in the affirmative, what biblical passages support our answers? How much can we change the Lord’s Supper before it ceases to be the Lord’s Supper? Although our Lord is gracious and often overlooks our faults, we have no authority from God to believe that a ceremony in which grape juice is given and received is really the Lord’s Supper.