"Soliloquy of the Spanish Cloister" begins and ends with an actual, guttural g-r-r-rowl of utter hatred, so you better believe "hate" is our number one theme! The speaker simply cannot stand his fellow monk, Brother Lawrence. In the first stanza of the poem, he watches the object of his hatred walk by, growling, "If hate killed men, Brother Lawrence,/ God's blood, would not mine kill you!" That's some pretty intense loathing right there – way stronger than your run-of-the-mill jealousy. So why does the speaker hate Brother Lawrence so much? Where does this intense hatred come from? Is it jealousy, or does it really spring from the petty doctrinal differences of religious practice that the speaker describes?
The speaker's intense hatred of Brother Lawrence is a product of his zeal for petty doctrinal rules, which he thinks Brother Lawrence to be too lax about observing.
In "Soliloquy of the Spanish Cloister," hatred seems to be a product of the speaker's extreme repression and frustration with the claustrophobia of monastic life.