The speed of light, we know, is the universe’s speed limit. Nothing can move faster than that through space.
Are we missing the point? Maybe it’s not so much that that’s the top speed through space; maybe that’s the only speed through spacetime, and everything is moving at it — you, me, light, trains, turtles, mountains, everything, always. “Slower” things are moving at the speed of light more in the time direction of spacetime than in the space direction. “Faster” things are moving at the speed of light more in the space direction of spacetime than in the time direction. What we call “acceleration” is (I speculate) nothing other than changing the direction of your constant motion, more timeward or more spaceward. Non-spaceward motion (i.e., standing still) is what we experience as the ordinary passage of time.
If this is anything like right, then it supplies an intuitive foundation for thinking about all kinds of weird mysteries: why the speed of light is a constant in all reference frames (the paradox that got Einstein thinking about relativity in the first place); what’s special about acceleration; and time dilation and the physical basis of the Lorentz transformation.