If you were heading due north at 100m/s, then changed your bearing to head slightly east without changing your overall speed, then you'd now be heading a bit less than 100m/s north and a bit more than 0m/s east.
This is the same kind of thing, except that when "at rest" in space (relative to some fixed point) you're moving at the speed of light in a pure time direction. When you move in space, you divert some of that speed from the time direction into the space direction you're moving in. Overall you're still doing the speed of light, just in a different "direction".
This is the same kind of thing, except that when "at rest" in space (relative to some fixed point) you're moving at the speed of light in a pure time direction. When you move in space, you divert some of that speed from the time direction into the space direction you're moving in. Overall you're still doing the speed of light, just in a different "direction".