Therefore he says This also, I saw, is from the hand of God. This is a noteworthy statement and an outstanding doctrine, but he stresses it less than he did the earlier one. This is because an affirmative statement affects us less than a negative one, as, for example, even the affirmative statement “I am the Lord your God, who brought you out of the land of Egypt” (Ex. 20:2) is quickly said but does not affect us, while there is greater force in the negative statement “You shall have no other gods before Me” (Ex. 20:3). Thus here also he treats the affirmative statement “It is good for a man to eat, etc.” in few words; but he uses many words in the negative statement, to prove and show us our foolishness, namely, that we accomplish nothing by all our counsels and our toil, distracted as we are by anxiety so that we do not use the things that are present. To crude people it is necessary that he speak in crude and lengthy terms and with examples. To wise people he could have said it all in one word: “The Lord Himself is your God.”
Eccl. 2:25. For who has eaten or enjoyed himself more than I?
He is citing his own experience. “For if I who achieved many things and had an abundance of good things still have not attained what I wanted, how much less will others do so if God does not grant happiness?” (Luther’s Works, v.15 p.47)