An expansion of NATO will strengthen the functions of NATO. It will allow for NATO to have more power and allow NATO to make quicker decisions on the things that matter most. If NATO stays the way they currently are, they will be very limited in the functions that they have.
NATO is the North Atlantic Treaty Organization, and it was an organization, or an alliance to help end the second world war. By expanding to more and more countries, it would only help spread the idea of world peace by having a one world alliance. Hopefully this would help avoid any more war.