does not listen to the words of mine that he speaks in my name

Here "my name" represents Yahweh and his authority. AT: "does not listen to him when he speaks my message" (See: rc://en/ta/man/translate/figs-metonymy)

require it of him

"I will hold him responsible" or "I will punish him." Here "him" refers to the person who does not listen to the prophet.