Final answer:
John Wesley's life was changed by a deep religious conversion experience in 1738 that led him to preach about a personal relationship with God.
Step-by-step explanation:
The experience that changed everything for John Wesley was a deep religious conversion that he and his brother, Charles, both experienced in 1738. This conversion led them to preach about a personal, emotional relationship with God, which also carried over to the colonies. The Wesleys were influenced by the writings of Martin Luther, specifically his concept of Justification by Faith, and the Moravians, a Protestant group with German roots. This experience propelled John Wesley to become a prominent figure in the Methodist movement.