Why are you to glorify God? - Because he made me and takes care of me.
What I hate most about NFP is that it requires abstinence when the wife's wondrous libido is at it's glorious peak. The Creator designed the reproduction system to give pleasure and create children. It's pretty marvelous the way it works. It's so much better than the ways that any of the other creatures' work. It's sad that depraved mind seeks ways to foil such a benevolent and ingenious system.
It does seem almost capriciously cruel that by using NFP, the wife only has sex when she doesn't feel like it, and is not allowed to have sex whenever she actually is in the mood. My own personal observation, is that there are probably subliminal signals that tell the husband when his wife is fertile which stimulates his libido as well. It could be psychological, such as her behaviour when she is experiencing fertility, or it could be physiological, such as scent, etc. In any case, it makes NFP seem not very "natural."