Matthew 18:2 And Jesus called a little child unto him, and set him in the midst of them,
Matthew 18:3 And said, Verily I say unto you, Except ye be converted, and become as little children, ye shall not enter into the kingdom of heaven.
Matthew 18:4 Whosoever therefore shall humble himself as this little child, the same is greatest in the kingdom of heaven.
Matthew 18:5 And whoso shall receive one such little child in my name receiveth me.
Matthew 18:6 But whoso shall offend one of these little ones which believe in me, it were better for him that a millstone were hanged about his neck, and that he were drowned in the depth of the sea.
Verse 2 a child is being called to Jesus as a demonstration. This child is set in the midst of the disciples.
Verse 3 is Jesus explaining that we are saved through faith, converted by child like faith, becoming like a child to enter into the kingdom of heaven.
Verse 4 is becoming humble, humble as a child is humble, with children there seems to be non greater or lesser, they are all equals in their site and thinking, and this is compared to heaven. Who is greatest in heaven Paul, John the Baptist, or the widow woman with 2 mites? We all have our favorite.
Verse 5 is a call to receive a child. Here is this verse seems to be receiving a person that has become as a little child and we are to receive them, by doing so we receive Jesus, not unto salvation, but as one of the family. As we see in other scripture as well, the receiving of a child is encouraged; see Matthew 19:14 and children should be allowed to come to Jesus.
Verse 6 is a warning to those who offend a little one, whether it is a child in faith who has become a child and became born again, and if you please a child that wishes to receive Jesus as savior. To offend a little one is worse, as described in this verse, worse than having a millstone tied around their neck and cast into the sea to drown. Ananias had to make this choice when he was instructed to go to Saul and lay his hands on him; See Acts 9:13.