Imagining gravitational waves inevitably leads me to believe that gravity is a force that varies (in a cycle) over spacetime. But.. what exactly does it mean to

Imagining gravitational waves inevitably leads me to believe that gravity is a force that varies (in a cycle) over spacetime. But.. what exactly does it mean to propagate over a cycle in spacetime? (particularly the time aspect confuses me since something propagating in space remains constant in time (either accelerating or decelerating)