What is the meaning of sackcloth and ashes?

What is the meaning of sackcloth and ashes? How are sackcloth and ashes symbolic of repentance?

Why Ashes

sackcloth - Wiktionary, the free dictionary

The Spirit of Sackcloth and Ashes Is Much Needed - LetterPile

What is unrepentance? What does it mean to be unrepentant?

Sackcloth And Ashes – Otosection

Sack-cloth and ashes – Historical articles and

What Does it Mean That There Will Be Beauty for Ashes? (Isaiah 61:3)

How long was Job's suffering?

Luke 10 Commentary