Today, the Gospel teaches us two lessons of Jesus, that are closely linked together. On the one hand, He tells them that «they will kill him, but three days after He has been killed, He will rise» (Mk 9:31). The Father's purpose for His coming to this world, was precisely this: to set us free from sin's slavery and eternal death; thus, we shall become the sons of God. Jesus' greatest form of submission —His death on the cross— shows God's infinite love for humanity: a measureless Love, a Love that does not mind facing the madness and scandal of the Cross.
On the other hand, it is terrifying, to see the Apostles' reaction. They were just too busy thinking of themselves only and forgetting to learn from their Master: «The disciples, however, did not understand these words» (Mk 9:32), because they had been arguing on the way about who was the greatest, and they were afraid to ask Him anything, lest they could be scolded.
With delicate patience, Jesus adds: let him be last of all and servant of all. We have to look for the simple and small, because the Lord identified Himself with them. We have to receive Jesus in our life; thus, we shall be opening the doors to the very same God. It is like programming our life to keep on going.
This is how the holy Rector of Ars, John Baptist Mary Vianney explains it: «Each time we put the needs of others above our own, and provided this does not go against God's Law, we are achieving merits God only knows about». Jesus teaches with these words, but mostly He teaches with His deeds. Those Apostles, who were, in principle, supposed to understand him, but did not quite, after the Cross and Resurrection, will follow in the footsteps of their Lord and their God. And, accompanied by the Holy Virgin Mary, they will grow smaller and smaller every day to let Jesus grow in them and in the world.