John Gill Commentary Ecclesiastes 6:3

"If a man beget a hundred children, and live many years, so that the days of his years are many, but his soul be not filled with good, and moreover he have no burial; I say, that an untimely birth is better than he:" — Ecclesiastes 6:3 (ASV)

If a man beget an hundred [children]
Sons and daughters, a certain number for an uncertain. Some have had many children, and almost this number; Rehoboam had twenty eight sons and threescore daughters; and Ahab had seventy sons, how many daughters is not said, (2 Chronicles 11:21) (2 Kings 10:1) ; this was reckoned a great honour and happiness to have many children; happy was the man that has his quiver full of them, (Psalms 127:3) ; such a case is here supposed;

and live many years, so that the days of his years be many ;
or "sufficient", as Jarchi interprets it; he lives as long as life is desirable; lives to a good old age, to the full age of men, threescore years and ten; yea, supposing he was to live to be as old as Methuselah,

and his soul be not filled with good ;
does not enjoy the good things he has; has no pleasure nor satisfaction in the temporal good things of life, has not the comfort of them, and is always uneasy, because he has not more of them; and especially if his soul is not filled with spiritual good things, the grace of God, and righteousness of Christ;

And also [that] he have no burial ;
as Jezebel, Jehoiakim, and others; who is either destroyed by robbers and cutthroats, for the sake of his substance, and cast into a ditch or a river, or some place, where he is never found to be interred; or else, being of such a sordid disposition, he provides not for a decent burial, suitably to his circumstances, or forbids one; or, being despised and disesteemed by all men, his heirs and successors either neglect or refuse to give him one; see (Jeremiah 22:29) ;

I say [that] an untimely birth [is] better than he ;
an abortive is to be preferred unto him; it would have been better for him if he had never been born, or had been in such a case.