From the Gospel according to Mark
MK 9:30-37

Jesus and his disciples left from there and began a journey through Galilee, but he did not wish anyone to know about it.  He was teaching his disciples and telling them, “The Son of Man is to be handed over to men and they will kill him, and three days after his death the Son of Man will rise.”  But they did not understand the saying, and they were afraid to question him.

They came to Capernaum and, once inside the house, he began to ask them, “What were you arguing about on the way?”  But they remained silent. For they had been discussing among themselves on the way who was the greatest. Then he sat down, called the Twelve, and said to them,  “If anyone wishes to be first, he shall be the last of all and the servant of all.”  Taking a child, he placed it in their midst, and putting his arms around it, he said to them, “Whoever receives one child such as this in my name, receives me; and whoever receives me, receives not me but the One who sent me.”