"Against you is for you" (καθ' υμων υπερ υμων). Mark 9:40 has "against us is for us" (ημων ... ημων). The Koine Greek η and υ were often pronounced alike and it was easy to interchange them. So many MSS. here read just as in Mark. The point is precisely the same as it is a proverbial saying. See a similar saying in Luke 11:23: "He that is not with me is against me." The prohibition here as in Mark 9:39 is general: "Stop hindering him" (μη κωλυετε, μη and the present imperative, not μη and the aorist subjunctive). The lesson of toleration in methods of work for Christ is needed today.