The second commitment is to interpretive humility, the view that the authors one is reading and interpreting are, in an important sense, wiser than oneself. When this principle is added to the first then one has specific reasons to work to try to find out the "genius" of the text one is interpreting in order to work out the basis of its significant contribution to the discipline one is engaged with.
Now if these are the principles of Rawls' hermeneutics in a general sense, Frazer contrasts them with a philosophical commitment that, in a sense, undercuts the hermeneutic principles (at least that of interpretive humility). This philosophical commitment is Rawls' modest conception of the role and import of political philosophy, political-philosophical humility, a humility that deflates the place of political philosophy viewing it as, at most, a part of the background conditions for public reason to be effective. However, to this general view of the role of political philosophy is also attached the specific way Rawls understands this modesty with regard to the place of political philosophy. The modesty is defined in terms of viewing political philosophy in the terms that emerged after the "Kantian constructivist" period when Rawls stressed the notion that political philosophy is "political, not metaphysical". This claim requires political philosophy to abstain from commitments with regard to profound existential questions of political life.
Now Frazer's general point is that if you hold, as Rawls did, to such a clear form of political-philosophical humility then you will often have trouble, when interpreting texts, in viewing them through the lenses of interpretive humility when you realise that these authors do not share your view of political-philosophical humility. This tension can be resolved in one of two possible ways. On the one hand, you can interpret the authors according to a notion of interpretive charity and include in your notion of interpretive charity the view that any reasonable author will implicitly or explicitly include in their approach a form of political-philosophical humility even if not one quite as specific as the view that political philosophy should be "political, not metaphysical". This resolution of the tension between interpretive humility and political-philosophical humility by means of interpretive charity has odd results however, implying as it does anachronistic views of the task of political philosophy. The other form of resolution would be to accept that the authors in question do not fit your model of political-philosophical humility but in that case you can no longer be committed to the notion of interpretive humility with regard to these authors given your conviction of the superiority of the approach of political-philosophical humility.
Frazer's review in raising these questions about Rawls' response to the history of philosophy has the important effect of posing a problem for those, like Rawls, who are committed to the view that the interpretation of the history of philosophy has to be, in the first instance, philosophical rather than historical. If one is committed to this view then the standards that one regards as philosophically apt will tend to have the possible effect of distortion of the texts in question. To view the interpretation of philosophical texts, by contrast, as including a commitment to finding the historical basis of the texts' positions as a matter of first priority need not imply that one is not also engaged in a philosophical task though it may lead one to understand the task of philosophy as something that cannot be assumed to fit a method most suitable or convenient to oneself.