Arrow is a show pretty much entirely about penance, as they remind us with Oliver over and over again. This time around, however, they are naming an episode Penance because of Diggle, with a bit of Felicity mixed in. With Oliver's PTSD and self-loathing/sabotage subdued for the time being, the gap is being filled by Diggle's insistence on staying in military jail and Felicity's Havenrock spiral continuing around sole survivor Rory/Ragman.