Nichiren explains the phrase, "I am the only person who can rescue and protect others"

"This is why the second volume of the Lotus Sutra states: 'But now this threefold world is all my domain, and the living beings in it are all my children. Now this place is beset by many pains and trials. I am the only person who can rescue and protect others, but though I teach and instruct them, they do not believe or accept my teachings.'

This passage means that to us living beings the Thus Come One Shakyamuni is our parent, our teacher, and our sovereign. Although Amida, Medicine Master, and other Buddhas are sovereigns to us living beings, they are neither parents nor teachers. Shakyamuni is the only Buddha endowed with all three virtues and to whom we owe a profound debt of gratitude. There are parents and there are parents, yet none of them can equal Shakyamuni Buddha. There are all manner of teachers and sovereigns, but none as admirable as he is. Could those who disobey the teaching of this paresutrant, teacher, and sovereign possibly not be abandoned by the heavenly gods and the earthly deities? They are the most unfilial of all children. It is for this reason that the Buddha said, “Though I teach and instruct them, they do not believe or accept my teachings.” Even if they follow the sutras preached before the Lotus and practice them for a hundred, a thousand, ten thousand, or a million kalpas, if they do not believe in the Lotus Sutra and chant Namu-myoho-renge-kyo even once, they will be unfilial. They will therefore be abandoned by the sacred ones of the three existences and the ten directions, and hated by both the heavenly gods and the earthly deities. (This is the first of the five guides for propagation.)"