I think what Jesus is saying makes sense in context if you look at the corresponding parallels in context. He is responding to the proposal by the mother of the two sons of Zebedee that they be seated on Jesus' left and right in his "kingdom." Of course, by "kingdom," they were thinking of Jesus displacing and physically sitting on the throne of Herod Antipas ("King of the Jews"), liberating them from Roman rule, and returning Israel to the former historical glory days of David/Solomon/etc. That was his disciples' and anyone else's mindset at the time. But go to verse 25 and you have: αρχοντες ("chiefs") of the nations κατα-κυριος (lord-down/against or "lord over") and μεγαλοι (the "great") κατα-εξοουσια (have authority down/against, or over). That is in parallel with the two propositions in verse 26 and 27, where we have μεγας becoming διακονος, and πρωτος (first, meaning foremost) being δουλος. The difference between διακονος and δουλος, of course, is that the former is a servant by choice and the latter by bondage. So we have both. And that parallels verse 28, where we have "the son of the man" corresponding back to διακονος, and his ψυχην (life, as in the life he was living) corresponding with αντι-λυτρον (a thing that looses, i.e. liberates, in the place/instead of πολλων, "many," who are in bondage, which would eventually be revealed/realized as bondage not to the Romans, but to sin and the Lord of sin, the devil).