"As a man comes, so he departs, and what does he gain, since he toils for the wind? All his days he eats in darkness, with great frustration, affliction and anger." (Ecc.5:16)
There can be little doubt that Ecclesiastes is indeed the eternal Word of God. It comes from the mouth of God just as Deuteronomy comes from the mouth of God, just as Romans and John 3:16 and Galatians 3:28 comes from the mouth of God.
Therefore, we have here, in the solid declaration of the meaninglessness, worthlessness, absurdity, and vacuity of everything which makes up life not first the results of one ancient near eastern philosopher's study but The Revelation of God. That life is meaningless is not something we can subject to debate or denial, for we are immediately thrust in this matter towards confesson or denial of the Word of God. To say that life has meaning is to deny God.