His saying sounds like an easy statement, but if read superficially it does not seem true. Has Jesus not also said, “Whoever is not with me is against me, and whoever does not gather with me scatters” (Matthew 12:30)? As a general rule it cannot be stated that all who are not opponents are supporters. Such a statement only makes sense when opposition to Jesus has become so general and self-evident that any exception to the general condemnation of him suggests as such already a favourable judgment about him. Verse 40 must be understood with reference to the times, and is coloured. Jesus says it at this time, when they are en route to his rejection by the people. Whoever is now not against Jesus (“Crucify him,” everyone will later call) is certainly for him. Disciples say of a Christian who casts out demons but does not follow them: this is not good! Jesus says, It is more than we might expect at this time!1
40 For the one who is not against us is for us.