The expression is derived from the Oriental custom of prostrating oneself with one's face to the ground before a high-ranking person. The meaning in this context is therefore that the man submits completely to the most exalted One who brought the suffering upon him (see notes elsewhere). It indicates his acceptance of God’s hand as the source of his suffering and expresses repentance (see also Job 42:6). Ultimately it also conveys his hope and dependence on God for mercy, because of God’s faithfulness and ultimate love for his people.1
29 Il mettra sa bouche dans la poussière, Sans perdre toute espérance;