Origen
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.
But how can he who has been converted, and become as a little child, be yet liable to be scandalized? This may be thus explained. Every one who believes on the Son of God, and walks after evangelic acts, is converted and walks as a little child; but he who is not converted that he may become as a child, it is impossible that he should enter into the kingdom of heaven. But in every congregation of believers, there are some only newly converted that they may become as little children, but not yet made such; these are the little ones in Christ, and these are they that receive offence.