Without a key, no one can open the door to a storehouse and see the treasures piled up in it. The Buddha first preached the Flower Garland Sūtra, in which He did not show the key to open its treasure house. The Buddha then expounded various sūtras such as the Āgama, Hōdō, Hannya sūtras, and the Sūtra of Meditation on the Buddha of Infinite Life during the forty years or so before preaching the Lotus Sūtra. However, these were all expedient, without revealing the true intent of the Buddha, and the doors to them remained closed. As a result, no one ever understood them; or even if someone claimed to have understood them, that person was wrong.
However, the Buddha finally expounded the Lotus Sūtra to open the door to the storehouse loaded with the various sūtras. This was the time when the storehouse of various sūtras that had been closed for 40 years or so was opened and the treasures inside were seen by the people in the nine realms thanks to the key of the Lotus Sūtra. For example, while there are humans, other animals and plants on earth, no one with good eyes could see their colors and shapes without the light of the sun and moon. Only when the sun and moon rise, can we see their colors and shapes. The various sūtras before the Lotus Sūtra are like the darkness of the night while the essential and theoretical sections of the Lotus Sūtra are like the sunlight and moonlight. Many bodhisattvas with two eyes, the Two Vehicles with slanted eyesight and ordinary people and men of icchantika with poor eyesight all could not see anything clearly in the various pre-Lotus sūtras, much less the colors and shapes of those sūtras. Thanks to the Lotus Sūtra, the two eyes of bodhisattvas were first opened with the help of the moonlight of the theoretical section of the Lotus Sūtra. These were followed by the eyes of the Two Vehicles, ordinary people, and icchantika, which were gradually opened to gain the seed for future Buddhahood. These were due entirely to the merit of the single Chinese character myō.
Hokke Daimoku Shō, Treatise on the Daimoku of the Lotus Sūtra, Writings of Nichiren Shōnin, Faith and Practice, Volume 4, Page 41-42