Merely intellectual scepticism, however, is not within Isaiah's horizon. He would never have employed (nor would any other prophet) our modern habits of doubt, except as he employs these intellectual terms, _to know_ and _to consider_--viz., as instruments of moral search and conviction. Had he lived now he would have been found among those few great prophets who use the resources of the human intellect to expose the moral state of humanity; who, like Shakespeare and Hugo, turn man's detective and reflective processes upon his own conduct; who make himself stand at the bar of his conscience. And truly to have doubt of everything in heaven and earth, and never to doubt one's self, is to be guilty of as stiff and stupid a piece of self-righteousness as the religious formalists whom Isaiah exposes. But the moral of the chapter is plainly what we have shown it to be, that a man cannot stifle doubt and debate about his own heart or treatment of God; whatever else he thinks about and judges, he cannot help judging himself.
_Note on the Place of Nature in the Argument of the Lord._--The office which the Bible assigns to Nature in the controversy of God with man is fourfold--Assessor, Witness, Man's Fellow-Convict, and Doomster or Executioner. Taking these backward:--1. Scripture frequently exhibits Nature as the _doomster of the Lord_. Nature has a terrible power of flashing back from her vaster surfaces the guilty impressions of man's heart; at the last day her thunders shall peal the doom of the wicked, and her fire devour them. In those prophecies of the book of Isaiah which relate to his own time this use is not made of Nature, unless it be in his very earliest prophecy in chap. ii., and in his references to the earthquake (v. 25). To Isaiah the sentences and scourges of God are political and historical, the threats and arms of Assyria. He employs the violences of Nature only as metaphors for Assyrian rage and force. But he often promises fertility as the effect of the Lord's pardon, and when the prophets are writing about Nature, it is difficult to say whether they are to be understood literally or poetically. But, at any rate, there is much larger use made of physical catastrophes and convulsions in those other prophecies which do not relate to Isaiah's own time, and are now generally thought not to be his. Compare chaps. xiii. and xiv. 2. The representation of the earth as the _fellow-convict_ of guilty man, sharing his curse, is very vivid in Isaiah xxiv.-xxvii. In the prophecies relating to his own time Isaiah, of course, identifies the troubles that afflict the land with the sin of the people, of Judah. But these are due to political causes--viz., the Assyrian invasion. 3. In the Lord's court of judgement the prophets sometimes employ Nature as _a witness_ against man, as, for instance, the prophet Micah (vi. 1, _ff_). Nature is full of associations; the enduring mountains have memories from old, they have been constant witnesses of the dealing of God with His people. 4. Or lastly, Nature may be used as the great _assessor_ of the conscience, sitting to expound the principles on which God governs life. This is Isaiah's favourite use of Nature. He employs her to corroborate his statement of the Divine law and illustrate the ways of God to men, as in the end of chap. xxviii., and no doubt in the opening verse of this chapter.