Symbolism of Dust and Ashes
"Scripture frequently portrays dust and ashes as symbols of humility, mortality, and repentance. For instance, in Job 42:6, Job says, “Therefore I retract my words, and I repent in dust and ashes.” This act demonstrates a recognition of one’s lowly state before a holy God. Dust reminds believers that they do not possess eternal physical life on this earth, but that they depend entirely on their Creator for both existence and salvation.
Ashes, historically, also signified mourning or sorrow over one’s condition and the world’s fallen state. Examples in Scripture include times of national lament and personal grief (e.g., Daniel 9:3, Esther 4:1). Together, dust and ashes vividly depict human frailty and the need for divine intervention." BH