One mustn't have human affections—or rather one must love every soul as if it were one's own child. The passion to protect must extend itself over a world—but he felt it tethered and aching like a hobbling animal to the tree trunk. He turned his mule south.
This quote, from Chapter One of Part II, very nicely illustrates the fine line that exists between the desire for spiritual perfection and the possibility that the attainment of that perfection is inhuman. The priest feels guilt about how much love he has for his daughter, wishing that he had the selflessness to love all members of the human race without partiality. Even if he doesn't recognize it, however, we realize that the priest's love for his daughter—while perhaps not the all-embracing love he seeks—is one of the most admirable, praiseworthy and human responses he has to almost anything in the novel. This is an implicit question throughout the novel and one that Greene himself perhaps doesn't have the answer to: to what extent are humans obliged to break free from ordinary, habitual responses and seek something loftier, and when is it better to accept one's fallible human nature as it is? The quote is also interesting for the "hobbling animal" metaphor it employs. The metaphor evinces despair over the local, limited nature of his love by comparing it to a creature that cannot move at all, but the priest then "turned his mule south." That is, he moves much more slowly across the landscape than he imagines he should, but he is still moving. Greene subtly shows us the slight, but important, discrepancy between the priest's self-conception and what he really does.