Qoheleth now addresses the matter of injustice. Continuing his emphasis on sets of opposites and a proper place and time for each event of life, he now suggests that there is a time established for injustice and justice. Presently he is sensitive to oppression (4:1-3) and injustice in juridical procedures under the sun (3:16). But God has established a time when he will administer justice (v. 17). Injustice, like all earthly evils, will not continue indefinitely.
God's toleration of injustice has a purpose. It is to show people that they are like the animals (3:18). The presence of injustice in the world (v. 16) along with the fact of human mortality (v. 19) places humans at the level of beasts. Qoheleth notes that as we have come from dust, so we return to dust (v. 20). Observations made under the sun do not reveal to him whether the human spirit will survive death. Strong affirmations about life after death are reserved for the NT.