The title "Penance" refers most directly to John Diggle. Trapped in a cycle of self-loathing following the death of his brother, Andy, Diggle believes he deserves to be in prison—not for the crime he was framed for, but for the one he actually committed.
The core of the episode revolves around Oliver Queen’s decision to break John Diggle out of a military prison. This mission creates a sharp ideological divide between Oliver and his new recruits. For the first time, the "New Team Arrow"—Wild Dog, Artemis, and Curtis—actively opposes Oliver, even going as far as to physically intercept him. [S5E4] Penance
"Penance" is an essential chapter in Arrow’s "return to form" in Season 5. It successfully bridges the gap between the show’s past (the original Team Arrow bond) and its future (the new recruits). By the end of the hour, the lines of loyalty are redrawn: Oliver has his brother back, but the trust with his new team is fractured. It leaves the viewer with the haunting realization that while some debts can be paid, the cost of penance often leaves lasting scars on everyone involved. The title "Penance" refers most directly to John Diggle