The most important practice is the practice of faith.

"The meaning of this passage is that, although you may not hold in your hand the eight scrolls that make up the Lotus Sutra, if you are a person who has faith in the sutra, then all twenty-four hours of the day you are one who “upholds the sutra.” Though your mouth may not utter the sounds of one who is reciting the sutra, if you have faith in the Lotus Sutra, then every day, every hour, every instant you are one who reads all the sutras." -- Nichiren

"The Lotus Sutra, wherein the Buddha honestly discarded expedient means, says that one can 'gain entrance through faith alone.' And the Nirvana Sutra, which the Buddha preached in the grove of sal trees on the last day of his life, states, 'Although there are innumerable practices that lead to enlightenment, if one teaches faith, then that includes all those practices.'

"Thus faith is the basic requirement for entering the way of the Buddha. In the fifty-two stages of bodhisattva practice, the first ten stages, dealing with faith, are basic, and the first of these ten stages is that of arousing pure faith. Though lacking in knowledge of Buddhism, a person of faith, even if dull-witted, is to be reckoned as a person of correct views. But even though one has some knowledge of Buddhism, if one is without faith, then one is to be considered a slanderer and an icchantika, or person of incorrigible disbelief." -- Nichiren

"What is most important is that, by chanting Namu-myoho-renge-kyo alone, you can attain Buddhahood. It will no doubt depend on the strength of your faith. To have faith is the basis of Buddhism. Thus the fourth volume of Great Concentration and Insight states, “Buddhism is like an ocean that one can only enter with faith.” The fourth volume of The Annotations on “Great Concentration and Insight” explains this: “With regard to the phrase ‘Buddhism is like an ocean that one can only enter with faith,’ even Confucius taught that faith is first and foremost. How much more so is this true of the profound doctrines of Buddhism! Without faith, how could one possibly enter? That is why the Flower Garland Sutra defines faith as the basis of the way and the mother of blessings.” The first volume of Great Concentration and Insight says, “How does one hear, believe in, and practice the perfect teaching to attain perfect enlightenment?” The first volume of On “Great Concentration and Insight” says, “To ‘believe in the perfect teaching’ means to awaken faith through doctrine and to make faith the basis of practice.” -- Nichiren

"...In describing the first, second, and third of the five stages of practice, the Buddha restricts those at these stages from practicing precepts and meditation, and places all emphasis upon the single factor of wisdom. And because our wisdom is inadequate, he teaches us to substitute faith for wisdom, making this single word “faith” the foundation. Disbelief is the cause for becoming an icchantika and for slander of the Law, while faith is the cause for wisdom and corresponds to the stage of hearing the name and words of the truth."

"Both practice and study arise from faith." -- Nichiren

The blessings gained by arousing even a single moment of faith in and understanding of the Lotus Sutra surpass those of practicing the five prāmitās;..." -- Nichiren

"In this passage of commentary, “subordinate concerns” refers to the five pāramitās. If the beginner tries to practice the five pāramitās at the same time that he embraces the Lotus Sutra, that may work to obstruct his primary practice, which is faith...." -- Nichiren