Adam Clarke on 1 Samuel 3:18

Samuel told him every whit - Our word whit, or wid, comes from the Anglo-Saxon, which signifies person, thing, etc.; every whit is every thing. The Hebrew את כל הדברים et col haddebarim, "all these words."

It is the Lord - He is Sovereign, and will do what he pleases; he is righteous, and will do nothing but what is just.

Let him do what seemeth him good - There is much of a godly submission, as well as a deep sense of his own unworthiness, found in these words. He also had sinned, so as to be punished with temporal death; but surely there is no evidence that the displeasure of the Lord against him was extended to a future state.