NOTES for Mat 18:1-5
The disciples ask Jesus who is considered greatest in the Kingdom of Heaven. This question resembles scholastic disputes about how many angels can fit on the point of a needle, because it is entirely theoretical. Without understanding what the Kingdom of God is, they argue about how its hierarchical ladder is arranged. In the same way, they divide the places at the Savior's right and left hand in the life of the age to come, without realizing that they are asking for martyrs' crowns.
Jesus' answer is astonishing in its childlike simplicity and utter practicality. He does not discuss with them what they cannot understand, but instead takes something familiar and close at hand as an example. Christ does not speak of angels and archangels; He takes a child and shows in that child the image of a citizen of His Kingdom. He does not support these theoretical discussions but speaks directly about what one must be like in order to enter it.