Eccl. 2:26.  For to the man who pleases Him God gives wisdom and knowledge and joy; but to the sinner He gives the work of gathering and heaping, only to give to one who pleases God. This also is vanity and vexation of spirit.

He proves that it is a gift of God to be content with the things that are present, for this is given to the man who pleases God with-out any preceding merits. He divides the world into the pious and the impious. In addition to other common gifts, especially wisdom and prudence, joy is conferred on the pious, because they are content with things that are present and are not vexed with thoughts and desires as the impious are. They acknowledge in joy and peace that they are intelligent and wise in administering their affairs. But the impious suffer affliction, so that they continually add more and more, heap things up, and yet are never satisfied. In addition, even if they have wisdom and skill, it is still so mixed with troubles that it becomes more of a punishment for them. They do not enjoy their labors when they till the fields or build, but others enjoy them and get happiness from them. What the impious work at and build is not used rightly by anyone except the pious. Thus what sinners heap up belongs to the pious, because only they use it with thanksgiving and joy, even when they have very little. The impious, on the other hand, for all their anxiety and trouble, do not even use it. In short, the pious truly possess the whole world, because they enjoy it with happiness and tranquility. But the impious do not possess it even when they have it. This is the vanity which the impious possess. (Luther’s Works, v.15 p.47-48)

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)