Jesus taught his disciples about who is for him and who is against him.

Mark 9:38-41

38 John said to Jesus, “Teacher, we saw someone who was expelling demons, ◄claiming he had authority from you to do that/while telling people that you have told him to do it►. So we told him to stop doing it because he was not one of us disciples.” 39 Jesus said, “Do not tell him not to do that! For no one will speak evilly about me just after he performs a miracle while saying that I have told him to do it. 40 Furthermore, those who are not opposing us are trying to achieve the same goals that we are. 41 Also think about this: Those who belong to me who help you in any way, even if they just give you a cup of water to drink because you follow me, the Messiah, will certainly be rewarded by God!”