In the Beginning, There Was Religion
Many of Leonardo's paintings concern religious subjects, and he even worked for the pope for a while. But what did Leonardo actually think of religion? Was he a true believer, or was he just another sheep in the flock?
Leonardo the Christian?
Most scholars believe that Leonardo was a practicing Christian. He spent much of his life working under the pope's influence, so his frequent meetings with the clergy probably influenced him. The facts here, though, are few and far between.
Little is known about Leonardo's religious upbringing. His grandfather arranged for his baptism, and the church of Santa Croce is said to contain the font where Leonardo was baptized. That fact alone supports the possibility that he was indeed raised in the Christian tradition. His father, Ser Piero da Vinci, was not a religious man by profession; he was a notary, and there is nothing to suggest that Leonardo's father was particularly religious. Some of Leonardo's early training may have come from local priests, but that is also not known for certain.
Given that Leonardo's grandfather appears to have been a religious man, it is likely that his father was at least nominally Catholic, and his mother was either Catholic or Jewish. There are stories that his mother had been a slave in the Middle East. She was probably an Italian peasant girl who may or may not have been of Jewish descent. In support of the rumors is her name, Caterina; that particular name was apparently a common choice of Jewish slaves when they converted to Christianity.
You Are What You Paint
We do know that Leonardo wasn't averse to painting biblical subjects. Many of Leonardo's paintings were of a religious nature, which was certainly to be expected while he was under the patronage of the Medici family. Baptism of Christ, Annunciation, and Madonna and Child with a Pomegranate are just a few examples of the religious themes Leonardo was commissioned to paint. Given the time and place, though, he probably didn't have any choice. Religion, power, and culture overlapped significantly during the Renaissance, and support of the clergy was an important part of any patron's lifestyle.