Reishis Chachmah (Anavah 3) writes, "The Chacham Reb Avraham HaLevi said that we can learn [the importance of] humility from earth. There isn't much that one can do with a chunk of earth. He certainly can't make an earthenware utensil from it. But the more the earth is ground and broken into tiny, separated particles, the more suitable it is for the person, who can use it for his needs. I say that this is alluded to in the words ונפשי כעפר לכל תהיה, 'My soul shall be like earth before all.' The more humiliation, the higher his soul will elevate."
The Maharshal (Brachos 17.) explains נפשי כעפר לכל תהיה, "I heard that everyone treads on earth, but afterwards, the earth will tread on top of all those who trampled it. I do the same with all my enemies."
This means that people walk on earth, but in the end, the earth will cover them. I am like earth. I am silent when my enemies speak against me, but in the end, I will be the one who will be on top.
Tosfos (Brachos 17.) explains the words נפשי כעפר לכל תהיה, "Just as earth is never destroyed, so may it be Your will that my children shouldn’t ever cease, as it states והיה זרעך כעפר הארץ, "Your children will be like the dust of the earth."