The Lord’s Supper was instituted:

1. That it might be a confirmation of our faith, or a most sure proof of our union and communion with Christ, who feeds us with his body and blood unto everlasting life, as truly as we receive these signs from the hands of the minister. This object is attained by all those who receive these signs in true faith:  for we so receive these signs from the hands of the minister, as if the Lord himself gave them unto us with his own hand. It is in this way that Christ is said to have baptized more disciples than John, when he, nevertheless, did it through his disciples (John 4:1).
2. That we may by the observance of it make a public confession of our faith, acknowledge our gratitude, and bind ourselves to constant thankfulness, and to the celebration of this benefit. Hence it is said:  “This do in remembrance of me.” “For as often as ye eat of this bread and drink of this cup ye do show the Lord’s death till he come” (Luke 22:19; 1 Cor. 11:26). This remembrance, or commemoration of Christ precedes and is taken for faith in the heart; after which we make a public confession, and acknowledgements of our thankfulness.
3. That it might be a public distinction, or badge, by which the true church may be known, and recognized from the world. The Lord has instituted this supper for none, but those who are his disciples.
4. That it might be a bond of love, declaring that all who partake of it aright, are made members of one body whose head is Christ. “For we being many are one bread, and one body; for we are all partakers of that one bread” (1 Cor. 10:17). Those now who are members of the same body have a mutual love one for another.
5. That the people of God who assemble in a public manner might be united together in the closest fellowship; for it was instituted to be observed in the congregation, whether there by many or few present. Hence Christ says, “Drink ye all of it,” and Paul says, “When ye come together to eat tarry one for another” (Matt. 26:27; 1 Cor. 11:33).

--Zacharias Ursinus, Commentary on the Heidelberg Catechsim, p. 379.