I found an article on this website addressing the very question you have, entitled Birth Control and NFP: What’s the Difference?
Here is the link: (There are numerous other articles on this link too.)
Here is a quote from the article:
“In the fertile days of a woman’s cycle, if there are serious reasons to avoid pregnancy, the couple respectfully steps back from the act of intercourse. In using birth control devices, however, they attack the meaning of the act — they do the action of intercourse and then undo part of it. In NFP, instead, they simply choose at times not to do the action in the first place.”