Thou, even thou, art to be feared: and who may stand in thy sight when once thou art angry? Thou, even thou, art to be feared - The Hebrew is simple, but very emphatic: אתה נורא אתה attah nora attah, "Thou art terrible; thou art." The repetition of the pronoun deepens the sense.
When once thou art angry? - Literally, From the time thou art angry. In the moment thy wrath is kindled, in that moment judgment is executed. How awful is this consideration! If one hundred and eighty-five thousand men were in one moment destroyed by the wrath of God, canst thou, thou poor, miserable, feeble sinner, resist his will, and turn aside his thunder!