The womb is a circle of power where a force of nature is formed. The womb has the power to create life. Life is a force of nature, and the circle of life starts in the womb.
Now pretend you're the mother. You'll need all the force you can muster to bring that baby into the world, so you grab hold of your special saber (せい) and slice it about in the air to give you the extra force you need.