Einstein didn't like Newton's idea that mass causes action at a distance through gravity, so he came up with his explanation that mass causes a curvature in space time. It sounds to me like Einstein is just moving the problem around. Instead of mass causing action at a distance, now we just have mass causing space to curve at a distance. The problem is still there. We still have the problem of how mass causes action at a distance. Now the action is the curvature of space.