Ecclesiastes 2:19

And who knoweth whether he shall be a wise [man] or a fool?
&c.] The king that should be after him, as the Targum, that should be his successor and heir; and so whether he would make a good or bad use of what was left; whether he would keep and improve it, or squander it away; suggesting, that could he be sure he would be a wise man that should come into his labours, it would be some satisfaction to him that he had laboured, and such a man should have the benefit of it; but as it was a precarious thing what he would be, he could take no pleasure in reviewing his labours he was about to leave. Some think that Solomon here gives a hint of the suspicion he had, that his son Rehoboam, his successor and heir, would turn out a foolish man, as he did; yet shall he have rule over all my labour wherein I have laboured, and
wherein I have showed myself wise, under the sun;
be he what he will, all will come into his hands; and he will have the power of disposing of all at his pleasure; not only of enjoying it, but of changing and altering things; and perhaps greatly for the worse, if he does not entirely destroy what has been wrought with so much care and industry, toil and labour, wisdom and prudence; the thought of all which was afflicting and distressing: and therefore he adds, This [is] also vanity;
and shows there is no happiness in all that a man does, has, or enjoys; and this circumstance, before related, adds to his vexation and unhappiness.