'Themselves' in the Bible

And I set my mind to seek and explore by [man’s] wisdom all [human activity] that has been done under heaven. It is a miserable business and a burdensome task which God has given the sons of men with which to be busy and distressed.

I have seen the task which God has given to the sons of men with which to occupy themselves.

I said to myself regarding the sons of men, “God is surely testing them in order for them to see that [by themselves, without God] they are [only] animals.”

If the clouds are full [of rain], they empty themselves on the earth; and if a tree falls toward the south or toward the north, in the place where the tree falls, there it lies.

in the day when the keepers of the house (hands, arms) tremble, and the strong men (feet, knees) bow themselves, and the grinders (molar teeth) cease because they are few, and those (eyes) who look through the windows grow dim;