Jesus continues teaching the disciples that they need to be humble like a child if they want to be important in God's kingdom. (See: [[rc://en/ta/man/translate/figs-simile]])
The phrase "kingdom of heaven" refers to God's rule as king. This phrase is used only in the book of Matthew. If possible, keep "heaven" in your translation. AT: "in God's kingdom" or "when our God in heaven establishes his rule on earth" (See: [[rc://en/ta/man/translate/figs-metonymy]])
Jesus means that it is the same as welcoming him. AT: "When someone ... in my name, it is like he is welcoming me" or "When someone ... in my name, it is as if he were welcoming me"
# a great millstone should be hung about his neck, and that he should be sunk into the depths of the sea
This can be stated in active form. AT: "if someone put a great millstone around his neck and threw him into the deep sea" (See: [[rc://en/ta/man/translate/figs-activepassive]])