Connecting Statement:

Job continues speaking to his friends.

See, is not their prosperity in their own hands?

Here "hands" refers to their power or control. Job uses this question to challenge his friends. Alternate translation: "Look, these wicked people claim that they make themselves prosper!" (See: rc://en/ta/man/translate/figs-metonymy and rc://en/ta/man/translate/figs-rquestion)