For the living know that they shall die: but the dead know not any thing, neither have they any more a reward; for the memory of them is forgotten.

Wesley's Notes

9:5 Die - Whereby they are taught to improve life. Any thing - Of the actions and events of this world. Reward - The fruit of their labours in this world, are utterly lost as to them. Forgotten - Even in those places where they had lived in great power and glory.

Jamieson-Fausset-Brown Bible Commentary

5. know that they shall die-and may thereby be led "so to number their days, that they may apply their hearts to wisdom" (Ec 7:1-4; Ps 90:12).

dead know not anything-that is, so far as their bodily senses and worldly affairs are concerned (Job 14:21; Isa 63:16); also, they know no door of repentance open to them, such as is to all on earth.

neither . reward-no advantage from their worldly labors (Ec 2:18-22; 4:9).

memory-not of the righteous (Ps 112:6; Mal 3:16), but the wicked, who with all the pains to perpetuate their names (Ps 49:11) are soon "forgotten" (Ec 8:10).

Matthew Henry's Concise Commentary

9:4-10 The most despicable living man's state, is preferable to that of the most noble who have died impenitent. Solomon exhorts the wise and pious to cheerful confidence in God, whatever their condition in life. The meanest morsel, coming from their Father's love, in answer to prayer, will have a peculiar relish. Not that we may set our hearts upon the delights of sense, but what God has given us we may use with wisdom. The joy here described, is the gladness of heart that springs from a sense of the Divine favour. This is the world of service, that to come is the world of recompence. All in their stations, may find some work to do. And above all, sinners have the salvation of their souls to seek after, believers have to prove their faith, adorn the gospel, glorify God, and serve their generation.