The Sword God: Past and Future.
This quote is succinct with Zoro's growth as a swordsman. At the beginning, his aim was to become the best Swordsman for his own self interests, and while he still does now, what drives him is twofold. His original ambition, and the desire to become strong enough to protect things that are dear to him. Wano is sort of the apex to that development. Zoro is driven with the single minded goal of freeing Wano from the invaders that plague it. Particularly Kaido. He isn't doing it on behalf of someone like Luffy, he's not doing it to test his skills, it's a resolve he's developed from his time in the country and bonding with the people who've been exploited due to their lack of strength to make a change. His intentions are the purest among those on the roof.