In the Parable of the Magic City, the Buddha continues with his message explaining that all he had taught before the Lotus Sutra was only designed to get folks to the place where they would be able to understand and follow the Lotus Sutra. Because the Lotus Sutra is being taught the other teachings are not invaluable, nor are they to be discarded.
The teachings of Nirvana are not the final objective of Buddhist practice; it can be compared to the magic city the guide conjured in the Parable of the Magic City. If the Buddha had not taught Nirvana and instead opened his teaching career with the Lotus Sutra then people would have thought it was impossible and not have made the effort. The Buddha knew the road to the enlightenment equal to all Buddhas is a long and difficult path and he knew that the people of his time, his disciples, would not be able to complete the journey if he had started with that as the objective. As it is, even in their own lifetime his disciples could not attain enlightenment, they are only able to attain this after several lifetimes and only in places other than this Saha World.
Lecture on the Lotus Sutra