Westminster Shorter Catechism

Q. 96. What is the Lord's Supper?

A. 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.

Q. 97. What is required to the worthy receiving of the Lord's Supper?

A. It is required of them that would worthily partake of the Lord's Supper that they examine themselves of their knowledge to discern the Lord's body, of their faith to feed upon him, of their repentance, love, and new obedience; lest, coming unworthily, they eat and drink judgment to themselves.