Final answer:
John Wesley experienced a life-changing religious conversion in 1738 after reading Martin Luther's work on Justification by Faith, leading him to preach a personal and emotional relationship with God and influencing the Methodist denomination.
Step-by-step explanation:
The experience that changed everything for John Wesley was his deep religious conversion inspired by his reading of Martin Luther's work on Justification by Faith. In 1738, John and his brother Charles Wesley profoundly altered their paths after interacting with Moravian passengers upon their return to England from the American colonies as missionaries. This interaction led them to explore more deeply their own religious beliefs and the teachings of Luther, which emphasized a personal and direct relationship with God through faith alone, a stark departure from the traditional Anglican practices they were used to.
The Wesleys began preaching in a manner that reflected this new understanding, focusing on a personal connection with God rather than the formal and understated Anglican services. Their conversion experience led them to preach about an emotional relationship with God, which also influenced their practice of open-air revival preaching, resonating with many who felt disconnected from the established church. This pivotal moment not only shaped their own spiritual lives but also had a lasting impact on the formation of the Methodist denomination.