BG Chap 18 - Arjuna's nature to fight

Even though knowing fighting is his dharma, but being afraid of the sin of killing brāhmaṇas and gurus, Arjuna may not be inclined to fight. If Arjuna thus takes shelter of this false identity thinking he knows what is right and what is wrong, such resolve is useless. By his natural eagerness to fight, Arjuna would definitely fight because that is his nature. Actually he was considering himself master of his actions, as if he were directing the good and bad results of such work. He forgot that the Supreme Personality of Godhead was present there, instructing him to fight. That is the forgetfulness of the conditioned soul. The Supreme Personality gives directions as to what is good and what is bad, and one simply has to act in Kṛṣṇa consciousness to attain the perfection of life. Arjuna’s actions as a kṣatriya arise from his impressions, which are manifested by the material energy of the Lord. Being bound by actions arising from his nature, Arjuna would helplessly fight against his will.