Den Beste gives a pretty blunt description of NATO’s original purpose in his Why is NATO?:
In other words, the purpose of NATO was to get the US to impose peace on Europe, because the Europeans couldn’t do it for themselves, and to protect Europe from the USSR, because the Europeans couldn’t do that for themselves either. And it worked, too.
Has it continued to work?
NATO was a mutual defense pact, where all members would rally when any member was attacked. After the attack against the US in September of 2001, NATO actually did invoke Article V for the first time in its history.
And except for the UK, no one did anything because of it, or at least no one did anything helpful. Rather than rallying for war, as those who wrote the NATO treaty had expected in such a case, and committing their armies and navies to fight along side ours, they tried to use the invocation of Article V to prevent the US from fighting back. The mutual-defense pact had somehow been transformed into a mutual-surrender pact.