Ambrose of Milan
Catena Aurea · Lukasevangelium 9
Then there arose a reasoning among them, which of them should be greatest. And Jesus, perceiving the thought of their heart, took a child, and set him by him, And said unto them, Whosoever shall receive this child in my name receiveth me: and whosoever shall receive me receiveth him that sent me: for he that is least among you all, the same shall be great. And John answered and said, Master, we saw one casting out devils in thy name; and we forbad him, because he followeth not with us. And Jesus said unto him, Forbid him not: for he that is not against us is for us.
Now John is not blamed, because he did this from love, but he is taught to know the difference between the strong and the weak. And therefore our Lord though He rewards the stronger, yet does not exclude the weak; as it follows, And Jesus said unto him, Forbid him not, for he that is not against you is for you. True, O Lord. For both Joseph and Nicodemus, through fear Thy secret disciples, when the time came, did not refuse their offices. But still since Thou saidst elsewhere, He that is not with me is against me, and he that gathereth not with me scattereth, (Luke 11:23.) explain unto us lest the two seem contrary to one another. And it seems to me, if any one considers the Searcher of hearts, he cannot doubt that every man’s action is distinguished by the motive of his heart.