"But be not ye called Rabbi: for one is your Master, [even] Christ; and all ye are brethren. And call no [man] your father upon the earth: for one is your Father, which is in heaven. Neither be ye called masters: for one is your Master, even Christ." —Matthew 23:8-10
Brother Will sez:
These verses are pure equalitarianism. In a world without masters, there's no room for feudalism, capitalism, or any form of favoritism.
Churches will claim their head guy is Jesus's Number One on Earth, but the Biblical support for that can most kindly be called ambiguous. In the four canonical gospels and Acts, Jesus's followers are supposed to share the good news about what's become the French motto: liberty, fraternity, equality. It's true that the early church had leaders who were chosen by their communities to share knowledge, but that was simple intellectual communism: their teachings were free for everyone, and they were subject to the approval of the community.
"Call no man father" may be a greater refutation of hierarchy than "don't be called masters". It's certainly the most personal. It denies privilege in families and invalidates all forms of patriarchy.
Matthew 23:9 is awkward for churches that use paternal language. Their followers will doubletalk the point, but they can't point to Jesus making exceptions about who can be called father.
Quibbling about 23:9 often begins with the claim that of course it's okay to call your actual father "father." But Jesus rejects the idea that "actual" family matters:
"For whosoever shall do the will of God, the same is my brother, and my sister, and mother." —Mark 3:35
"If any [man] come to me, and hate not his father, and mother, and wife, and children, and brethren, and sisters, yea, and his own life also, he cannot be my disciple." —Luke 14:26
I agree with the scholars who say "hate" is a misleading translation. The meaning is that you should love God/Justice/Truth more than your family, and when you have to choose between them, God/Justice/Truth wins.