According to legend, Saint Patrick used a shamrock to explain about God. The shamrock, which looks like clover, has three leaves on each stem. Saint Patrick told the people that the shamrock was like the idea of the Trinity, that in the one God there are three divine beings: the Father, the Son and the Holy Spirit. The shamrock was sacred to the Druids, so Saint Patrick's use of it in explaining the trinity was very wise.
This is one of the many examples in the history of Christianity in which our religion has been flexible and used sacred symbols of other faiths to adopt/adapt to Christian beliefs. Too many Christians believe that Christianity cannot be flexible, open to different interpretations, or, heaven forbid, should be all inclusive. If early Christians had not adapted, then the loving religion that I have faith in would have never spread as it did.
Happy St. Patrick's Day!