Though use make you apt to kill me, Let not to that, self-murder added be, And sacrilege, three sins in killing three.

In line 16 and 17, the speaker essentially tells the listener that if they were to kill the flea, it would be a ot only self-murder, but the murder of three lives: their own, the speaker's, and the flea's. In line 18, the speaker places the flea on this holy pedestal, treating it as if it were sacred . By doing this, he makes it seem as though killing it would be a greater offense than it really is.