The author of Ecclesiastes, living centuries before the revelation of Jesus, the Resurrection and the Life (Jn 11:25), is naturally pessimistic about life. For example, he goes on and on about growing old. Then he speaks of death in six ways. Death is like going home, a snapped cord, a broken bowl, a shattered pitcher, a pulley fallen into a well, and dust returning to earth (Eccl 12:5-7). It isn't enough for him to say that we will die. He seems obligated to belabor the point.
Death, for the author of Ecclesiastes, almost ruins life. Death has a deadly sting; it is victorious over life (cf 1 Cor 15:55). Because of the overshadowing influence of death, we are tempted to trivialize life by eating and drinking, for tomorrow we die (1 Cor 15:32; Wis 2:5-6ff). Living for pleasure makes us slaves — slaves of sin through fear of death our whole lives long (Heb 2:15). Because of death, we are tempted to give "allegiance to the present age and to the prince of the air, that spirit who is even now at work among the rebellious. All of us were once of their company; we lived at the level of the flesh, following every whim and fancy, and so by nature deserved God's wrath like the rest" (Eph 2:2-3). Death can turn our lives into living deaths (see 1 Jn 3:14).
The only way to de-fang death is to believe in and live totally for Jesus, "the Resurrection and the Life" (Jn 11:25). Jesus alone holds "the keys of death and the nether world" (Rv 1:18). In Jesus, "death is swallowed up in victory" (1 Cor 15:54). Praise Jesus forever!