Gr-r-r – there go, my heart's abhorrence! (line 1)
Here we are, first line of the poem, and the speaker is already so disgusted that he can hardly form words – he actually growls to open the poem! He calls the as-yet-unnamed Brother Lawrence his "heart's abhorrence," reversing the usual poetic trope of addressing the speaker's beloved as his "heart's love" or "heart's joy."
If hate killed men, Brother Lawrence,God's blood, would not mine kill you! (lines 3-4)
The speaker admits that his hatred is intense enough to kill... if hate
actually worked that way. Isn't it kind of bad to hate a fellow monk
that much? Wouldn't that count as a sin?
Hell dry you up with its flames! (line 8)
The speaker intersperses delightful little oaths and swears like this
with his fake-polite remarks about Brother Lawrence's gardening.
Grumbling and swearing under your breath when you're angry at someone?
Yeah, that seems pretty realistic.