God gives some people wealth, possessions and honor, so that they lack nothing their hearts desire, but God does not grant them the ability to enjoy them, and strangers enjoy them instead. This is meaningless, a grievous evil.
Matthew Henry’s Concise Commentary
6:1-6 A man often has all he needs for outward enjoyment; yet the Lord leaves him so to covetousness or evil dispositions, that he makes no good or comfortable use of what he has. By one means or other his possessions come to strangers; this is vanity, and an evil disease. A numerous family was a matter of fond desire and of high honour among the Hebrews; and long life is the desire of mankind in general. Even with these additions a man may not be able to enjoy his riches, family, and life. Such a man, in his passage through life, seems to have been born for no end or use. And he who has entered on life only for one moment, to quit it the next, has a preferable lot to him who has lived long, but only to suffer.