Newton & Kepler: Effect & Cause?

I frequently make the point that science faith and one of the ways that I have found to illustrate this is to use Kepler's 1st Law: According to Kepler's First Law of Planetary Motion, planetary orbits are ellipses with the Sun at one focus of the ellipse. This means that even if they have the same size, ellipses with different shapes do not have the same center. My question is: what is the source of gravity at focus 2? Most people have no clue, which illustrates one aspect of science faith, which is that most people believe something that they don't understand and can't explain. They have faith that someone understands it, that it is understandable. They believe that it is fact, proven, and can be dismissed as unnecessary knowledge.