“himself.” Literally, “his soul,” but here meaning “himself.”
“eat of it.” To “eat” something was often idiomatic for fully experiencing and enjoying it. In Jeremiah 15:16, the prophet Jeremiah “ate” the words of God. Jesus said his followers would “eat” his flesh (John 6:48-58; see commentary on John 6:54).
“a stranger eats it.” What is unspoken is that the man has no heir, and this contrasts with Ecclesiastes 6:3 where a person has 100 children.
“pointless.” See commentary on Ecclesiastes 1:2.
“severe affliction.” The Hebrew word translated “severe” is from the root word for “evil,” which is why some English versions have “evil,” and the Hebrew word translated “affliction” can also be translated “sickness” or “disease.” The world is in a fallen state, under the influence of the Devil. It is indeed “sick” and in need of healing, which the Messiah will bring when he conquers the earth. There are many severe afflictions in this sick world. There is some similarity between Ecclesiastes 6:2 and Luke 12:16-21, in which Jesus spoke a parable about a rich man who did not live to enjoy his wealth. Life, and the ability to enjoy it, is uncertain; but what is certain is that if a person is rich toward God there will be a wonderful next life.