First, the paragraph is not entirely correct. In VNAV PATH the FMC uses pitch control to maintain a vertical path, but it will also apply thrust if the speed drops below the target speed.
Now to your question, what exactly are you not understanding ?
PATH is like following a line drawn in the sky from cruise FL to the airport (or an intermediate waypoint)
SPEED is totally different as it is a descent which follows a constant IAS (well usually a constant MACH followed by a constant IAS)