In the same way also he took the cup, after supper, saying, "This cup is the new covenant in my blood. Do this, as often as you drink it, in remembrance of me." For as often as you eat this bread and drink the cup, you proclaim the Lord's death until he comes. (1 Corinthians 11:25-26 ESV)
“So the Lord’s Supper was not just the idea of the apostles, not something conjured up by the Church, but it was a solemn command of the Lord. Why did He command them to keep it? Here is a most significant thing. I believe he gave this command in order to preserve the doctrine. This, you see is an enactment of the doctrine, it is a kind of display of the truth, and our Lord wanted to preserve the truth throughout the centuries until the end of the Christian era.
“What a wonderful thing this has been! This table with its bread and wine has often been a terrible condemnation of the pulpit. Men have entered pulpits and said that Jesus was only a man, that he was nothing more than a moral exemplar and a good teacher. They have said that his death was the death of a pacifist, that it was a great tragedy and that we must imitate his spirit and live in the same way. They have preached like that in pulpits and then they have gone down to the Communion table, and there has been no connection between their preaching and the message of that Communion service. The Communion table, the broken bread and the poured out wine, has been preaching a message.
“And so, because of men and their fallibility – and we are all fallible – the Lord took a step to preserve the truth, the doctrine. And if you want to know how to test modern teaching and modern preaching, here is your test: What relationship does it bear to the bread and the wine? Does it lead to that? Is the Communion service a demonstration of the message that has been preached? If it is not, the message has been false. Here is the Lord’s own command and he has commanded it in order to preserve the teaching.”
~ D. Martyn Lloyd-Jones, Authentic Christianity Vol. 1 (Crossway Books, 2000) p. 150