Rafiki, is very clear that it is one of the most important thing in the movie. The reason is that he would bring Simba to end the tyranny of Scar and besides, as the kingdoms of Simba and Zira would join as Rafiki Kiara and Kovu helped so they could be together and unite the kingdoms.
Yes, his wisdom saves the kindom several times, but he would be little more than a second rate support character if he wasn't a crazy baboon with a great kung-fu technique.