The answer
Job was a religious man, who feared and worshiped God according to His will; in everything governing himself according to the rules of the Divine Law. He was perfect, but not sinless; as he himself admits, "Though I were righteous, my own mouth would condemn me; though I were blameless, it would prove me perverse" (Job 9:20).God viewed his simplicity, sincerity, absence of guile or evil intention, and thorough fulfillment of the religious rites.
He was not absolutely sinless, or without any tendency to evil; as we see him complaining and demonstrating self righteousness. However, aware of his own weaknesses, he confesses them (Job 9:20); and repents of them. "I have heard of You by the hearing of the ear, But now my eye sees You. Therefore I abhor myself, and repent in dust and ashes" (Job 42:5-6).
God knows the heart of everyone. "For the Lord does not see as man sees; for man looks at the outward appearance, but the LORD looks at the heart" (1 Sam 16:7). He knows how righteous Job is, despite his complaints. David the prophet and king made many mistakes in his lifetime but he was described as "a man after His (God) own heart" (1 Sam 13:14).
Answered by His Eminence Metropolitan Youssef (opens in a new tab)