After Zarathustra spoke to the Dying Man (Jesus), he had to leave the town as people started to hate him, he was carrying a “dead dog”. I believe the dead dog is in the book a memory after the Dying Man, the memory of Jesus that is in Nietzsche's mind. Nietzsche kept the message and lessons that he got from Christ’s life; he was still full of faith that Jesus' message was truth, even though he was only a human.
Zarathustra’s companion (Jesus) is dead but he kept a memory, of him. Zarathustra realized that it was not about the “dead body” he was carrying, he says that he needs life companions not dead ones now, meaning, that after Jesus died his message should be applied to other people.
“Zarathustra shall not speak to the people but to companions”, equality in humans and mutual love and trust, then he says: “Zarathustra shall not be hands-man and dog to the hand!”, it is not about the power over other people or manipulation but equality.
Zarathustra is against hierarchies in churches, he says, “Behold the faithful of all faiths! Whom do they hate the most? Him who smashes their tables of values, the breaker, the law-breaker- but he is the creator.” In Nietzsche’s new belief the hierarchy of Christian Church does not matter, hierocratic structure of the church is not necessary. It was undermining the power and prestige of the Church, as an institution. As you can imagine the Church could not approve of this theory.
Zarathustra calls himself a creator of a new philosophy that seriously threats the power and position of the Church. He also decided to find people who would join him and spread the truth.
He says that “man is something that must be overcome: and for that reason you must love your virtues-for you will perish by them.” He speaks of himself as an enlightened. In the scene with a tree, he discovers that there is no point in being an inventor of a new truth if there is no one to share it with. And so he decided to do.
TBC in ‘Nietzsche about men and women in Thus Spoke Zarathustra’ post
The University of Winchester Journalism Course
History and Context of Journalism, Part IV,
Friedrich Nietzsche, Thus Spoke Zarathustra, Part 1