Hilary of Poitiers
Catena Aurea · Matthäusevangelium 18
At the same time came the disciples unto Jesus, saying, Who is the greatest in the kingdom of heaven? And Jesus called a little child unto him, and set him in the midst of them, And said, Verily I say unto you, Except ye be converted, and become as little children, ye shall not enter into the kingdom of heaven. Whosoever therefore shall humble himself as this little child, the same is greatest in the kingdom of heaven. And whoso shall receive one such little child in my name receiveth me. But whoso shall offend one of these little ones which believe in me, it were better for him that a millstone were hanged about his neck, and that he were drowned in the depth of the sea.
Mystically; The work of the mill is a toil of blindness, for the beasts having their eyes closed are driven round in a circle, and under the type of an ass we often find the Gentiles figured, who are held in the ignorance of blind labour; while the Jews have the path of knowledge set before them in the Law, who if they offend Christ’s Apostles it were better for them, that having their necks made fast to a mill-stone, they should be drowned in the sea, that is, kept under labour and in the depths of ignorance, as the Gentiles; for it were better for them that they should have never known Christ, than not to have received the Lord of the Prophets.