Able to receive Communion?

Are the mentally disabled allowed to take Communion? If not, why is this?

“Everyone ought to examine themselves before they eat of the bread and drink of the cup” (1 Corinthians 11:28).  Christians need to be able to examine themselves before receiving the Lord’s Supper.  That means being able to recognize they are sinners who have been redeemed by Jesus Christ, repent of their sins, and realize that in the sacrament they are receiving the Lord’s body and blood in, with and under the bread and wine.  Christians who cannot examine themselves in this way will be served the gospel of Jesus Christ in word only, for the strengthening of their faith and the forgiveness of sins.  Pastors will consider, on a case-by-case basis, how they will minister to Christians with intellectual and developmental disabilities.