Gravity

Gravity is caused by rotation of large objects.  Mass alone does cause gravity, but an object of large mass and surface area will cause gravity based on the speed of its rotation generating force.  This gravity will affect other bodies in space, causing moons and asteroids to rotate and orbit, which create their own less powerful gravity due to the smaller size of these objects.  Multiple small objects could form a loose surface area with some gravity generated from their speed and rotation.  

The Earth's gravity is not caused by a "spinning molten core," but by the rotation of the entire mass of earth causing gravitational force based on the size of its surface area.

Absense of rotation equals zero gravity.  If the Earth stopped rotating, we would all start floating towards space.

The Catholic Church was the established body of knowledge at the time, just as your Newtonian physics are now.  The idea of objects being attracted to each other "just because" is naive, ignorant, and absurd.  What causes this invisible force that remains such a mystery?  If there is such as force, called gravity, it needs to be generated by something.  Standing still = no output, therefore gravity is not a result of mass alone.  But if that mass is moving, then it can generate force.  That force is gravity.