Illustrate the theme of Ephesians 4:4, signifying the unity and universality of the Christian faith, with a respectful and devotional watercolor painting. Emphasize the feeling of harmony, peace and unity using traditional symbols of Christianity such as the Holy Cross, a dove symbolizing Holy Spirit, or hands held together in prayer. Be mindful not to use any text or words in this artwork. The overall tone should be serene, spiritual, and thought-provoking.