A.T. Robertson Commentary Mark 9:40

"For he that is not against us is for us." — Mark 9:40 (ASV)

He that is not against us is with us (ος ουκ εστιν καθ' ημων υπερ ημων εστιν). This profound saying throws a flood of light in every direction. The complement of this logion is that in Mt 12:30 "He that is not with me is against me." Both are needed. Some people imagine that they are really for Christ who refuse to take a stand in the open with him and for him.