finn is the foil to kylo ren, not rey. finn was taken from his family against his will into the first order and realized on his own that murder was wrong. conversely, kylo willingly went away from his family into the first order and consciously uses murder to gain power. as kylo kills his father, finn becomes a resistance hero. their storylines and development are inversely proportional to each other- when finn moves toward the light, kylo falls further toward darkness.