Smith is not content with a simple law-versus-grace distinction, nor will he say that Hosea brings something forward that Amos simply did not know. Amos is a true prophet and his account of God is true; God is as Amos says he is. What Smith is struggling with is a penetrating account of the theological reality of God, spoken of in one way by one prophet and spoken of in another way by a successor, but both men speaking truly. It is the subject matter of prophecy—the God to which the prophets refer—that concerns Smith. Even though the prophets may be distinctive figures to be ranged on a historical grid, they are affiliated at a level deeper than even their own grasp of the matter. Smith is convicted of this, and it is this specific theological gravity that keeps his reading drawn within the orbit of older concerns for affiliation, now in a new model that would threaten this aspect in other hands.
… The question is … : Why does Hosea form the lens through which our understanding of God—in relationship to Israel, the nations, time, and creation—is focussed? Why does his particular, comprehensive witness serve best in introducing first Joel and the Amos? Smith finds persuasive the arguments of historical criticism for the priority of Amos before Hosea. But in the end, it is the theologically expansive witness of Hosea that serves to illuminate the more partial account of Amos, in Smith's conception. In this manner, though he works with a fresh model of historical sequence, Smith has intuitively retained the insights that the canonical form itself sought to enforce (131-132, third emphasis original).This brings us to the key ingredient of the canonical approach as understood by Childs (see my article “Childs as Critical and Faithful Exegete,” though be careful with what I wrote in section 2! I'm rethinking that bit) : the witness of Scripture to a single divine reality. Seitz puts it thus:
My basic argument here is that the canonical form, when it is appreciated, even on the other side of historical accounts of priority, anteriority, and posteriority, serves to guard these kinds of crucial theological insights. The prophets are related, not in some easily reconstructed historical or sociological sense, but in the nature of their activity as spokesmen for God. … It is God himself who sees to the affiliation proper to his character, mediated through his servants the prophets (134, emphasis mine).