The most accurate statement regarding why Constantine I converted to Christianity during his fight to gain control of the Roman Empire is:
Constantine thought he saw a cross in the sky the night before a big battle and believed this celestial clue helped him win the battle.
This reflects the pivotal moment before the Battle of Milvian Bridge in 312 AD when Constantine reportedly had a vision of a cross. This experience, along with his subsequent victory, played a significant role in his conversion and support for Christianity.