Final answer:
During his first leave, Paul engaged with diverse cultures and religious practices in the Greco-Roman world, enriching his approach to spreading Christianity in different cities and influencing early Christian doctrine.
Step-by-step explanation:
Paul's experience during his first leave from his missionary work notably impacted his outlook and further endeavors in spreading Christianity. When Paul returned from his journey, his personal experiences with various cultures and religious practices in the Greco-Roman world enriched his understanding, allowing him to approach the dissemination of Christian teachings with a broader perspective. Engaging with cities like Ephesus, Corinth, Thessalonica, and Rome exposed Paul to a diverse array of beliefs, which played a crucial role in the development of early Christian doctrine and helped shape the way he preached and wrote about the faith.