John Lightfoot on Mark 9:38

[We saw one casting out devils in thy name.] I. Without doubt he truly did this work, whosoever he were. He cast out devils truly and really, and that by the divine power; otherwise Christ had not said those things which he did, "Forbid him not: for there is no man which shall do a miracle in my name, that can lightly speak evil of me," &c.

II. Whence then could any one that followed not Christ cast out devils? Or whence could any one that cast out devils not follow Christ?

I answer: We suppose,

I. That this man cast not out devils in the name of Jesus, but in the name of Christ, or Messias: and that it was not out of contempt that he followed not Jesus, but out of ignorance; namely, because he knew not yet that Jesus was the Messias.

II. We therefore conjecture that he had been heretofore some disciple of John, who had received his baptism in the name of the Messias now speedily to come, (which all the disciples of John had) but he knew not as yet that Jesus of Nazareth was the Messias: which John himself knew not until it was revealed to him from heaven.

III. It is probable, therefore, that God granted the gifts of miracles to some lately baptized by John, to do them in the name of the Messias; and that, to lay a plainer way for the receiving of the Messias, when he should manifest himself under the name of 'Jesus of Nazareth.'

See verse 41: In my name, because ye belong to Christ; and chapter 13:6, "Many shall come in my name"; not in the name of Jesus, but in the name of the Messias: for those false prophets assumed to themselves the name of the Messias, to bring to nought the name of Jesus. That, John 16:24, "Hitherto ye have asked nothing in my name," differs not much from this sense: 'The apostles poured out their prayers, and all the holy men theirs, in the name of the Messias; but ye have as yet asked nothing in my name Jesus,' &c.