In Hinayāna sūtras, the principle of inactive nirvana (ultimate goal of Hinayāna Buddhism to attain emptiness and tranquility) is the king, and wisdom is the king compared to observance of Hinayāna precepts and practice of Hinayāna meditation. In Mahāyāna sūtras, the principle of the Middle Way (non-duality) is the king. Also the Flower Garland Sūtra is the king in preaching the principle of perfect harmony and identity of all phenomena; the Wisdom Sūtra is the king in preaching the principle of voidness of all things; the Sūtra of the Great Assembly is the king in preaching to uphold the True Dharma; the Medicine Master Sūtra is the king in preaching the special vows of Medicine Master Buddha; the Sūtra of the Buddha of Infinite Life is the king in preaching the 48 vows of the Buddha of Infinite Life; and the Great Sun Buddha Sūtra is the king in preaching the finger signs (mudrā) and mantras; but none is the king of all sūtras preached during the Buddha’s lifetime. On the other hand the Lotus Sūtra is the great king who puts all the doctrines expounded in all the sūtras together and supervises them—such doctrines as absolute and relative reality, triple truth (truth of voidness, truth of temporariness and truth of the middle), finger signs (mudrā) and mantras, inactivity, 12 great vows of Medicine Master Buddha, and 48 vows of the Buddha of Infinite Life. I should say that he who understands this correctly knows the teaching.

Ken Hōbō-shō, A Clarificaton of Slandering the True Dharma, Writings of Nichiren Shōnin, Doctrine 3, Pages 131.