Who should be the greatest - See on Matthew 18:1-5 (note).

receive one.

Matthew 10:40-42 He that receives you receives me, and he that receives me receives him that sent me...

Matthew 18:3-5,10 And said, Truly I say to you, Except you be converted, and become as little children, you shall not enter into the kingdom of heaven...

Matthew 25:40 And the King shall answer and say to them, Truly I say to you, Inasmuch as you have done it to one of the least of these my brothers...

Luke 9:48 And said to them, Whoever shall receive this child in my name receives me: and whoever shall receive me receives him that sent me...

receive me.

Luke 10:16 He that hears you hears me; and he that despises you despises me; and he that despises me despises him that sent me.

John 5:23 That all men should honor the Son, even as they honor the Father. He that honors not the Son honors not the Father which has sent him.

John 10:30 I and my Father are one.

John 12:44,45 Jesus cried and said, He that believes on me, believes not on me, but on him that sent me...

John 14:21-23 He that has my commandments, and keeps them, he it is that loves me: and he that loves me shall be loved of my Father...

1 Thessalonians 4:8 He therefore that despises, despises not man, but God, who has also given to us his holy Spirit.

Unbelieving Belief
'And straightway the father of the child cried out, and said with tears, Lord, I believe; help Thou mine unbelief.'--Mark ix. 24. We owe to Mark's Gospel the fullest account of the pathetic incident of the healing of the demoniac boy. He alone gives us this part of the conversation between our Lord and the afflicted child's father. The poor man had brought his child to the disciples, and found them unable to do anything with him. A torrent of appeal breaks from his lips as soon as the Lord gives …
Alexander Maclaren—Expositions of Holy Scripture

July the Ninth Scholars in Christ's School
"He taught His disciples." --MARK ix. 30-37. And my Lord will teach me. He will lead me into "the deep things" of God. There is only one school for this sort of learning, and an old saint called it the Academy of Love, and it meets in Gethsemane and Calvary, and the Lord Himself is the teacher, and there is room in the school for thee and me. But the disciples were not in the mood for learning. They were not ambitious for heavenly knowledge, but for carnal prizes, not for wisdom, but for place. …
John Henry Jowett—My Daily Meditation for the Circling Year

The Lenten Fast.
"This kind can come forth by nothing, but by prayer."--ST. MARK ix. 29. You remember the narrative from which I have taken this verse. Jesus, as we read, had just come down from the Mount of Transfiguration, and when He was come to the multitude, a certain man besought him saying, "Have mercy on my son, for he is lunatic and sore vexed, and I brought him to Thy disciples, but they could not cure him." Then Jesus rebuked the devil, and the child was cured from that hour. Thereupon His disciples …
John Percival—Sermons at Rugby