He (i.e. God) hath cast me into the mire. "The mire" here is the lowest depth of misery and degradation (comp. Psalms 40:2; Psalms 69:2, Psalms 69:14). Job feels himself cast into it by God, but nevertheless does not forsake him nor cease to call upon him (verses 20-23).
And I am become like dust and ashes; i.e. unclean, impure, offensive to my fellow-men, an object of dislike and disdain.