The quality of being fast or quick.
Swiftnesses are usually good because it means things are happening quickly.
Examples:
The swiftnesses of the cheetah amaze me.
The swiftnesses of the rabbit help it escape from danger.
I admire the swiftnesses of the hummingbird.
The swiftnesses of the turtle are not as impressive as the swiftnesses of the hare.
The swiftnesses of the rocket are astonishing.
The swiftnesses of the superhero are legendary.