In other sects of Buddhism, statues or pictures of buddhas and bodhisattvas are usually adored as the object of worship. On the other hand, HBS adores Namu Myoho Renge Kyo, the sacred seven characters as the sole sublime Sacred Object (Gohonzon).
Nissen Shonin explaines the reason for this
The Honmon Butsuryu Shu (HBS) worships Namu Myoho Renge Kyo as the Sacred Object (Daimoku Honzon), that is, the great Mandala containing all the teachings in the universe, to which is given scriptural evidence in "The Supernatural Powers of the Tathagata" of the Lotus Sutra. All the teachings of the Tathagata are revealed and expounded explicitly in this sutra. "Nichiren Shonin said in his Shishin Gohon Sho that Myoho Renge Kyo does not represent the sutra text, nor is it the meaning, and that it is none other than the intent of the entire sutra. Further he said that this is not only an objective truth but also the world of immeasurable merits inherent in the minds of people engaged in practicing the Lotus Sutra. One's behavior and deeds are caused by the function of the mind. If we focus our minds on Namu Myoho Renge Kyo, the Sacred Object of Worship and chant the Odaimoku in order to shake off delusion and calm our minds, we will be able to obtain an unwavering view of life, never fearing to die, and returning to one's right mind. This is indeed the great way directly leading to the state of Buddhist enlightenment by sheer force of faith. If everyone thus returns to the Buddha mind, there will be no one who strays from the path of righteousness; accordingly the ideal of a peaceful world will be attained. The day will soon come when those who accumulate day and night the merits of their pious acts or religious practice will enjoy visiting the Pure Land. Confucianism also teaches as follows: it depends on whether each person's heart is in the right place or not that peace reigns over the realm. Much more Buddhism is the teaching which sets people right by the law of cause and effect in the past, present, and future, thus improving the present world and promising the security for life after death. That is why one Buddha or one Saint is not enshrined and worshipped in our sect, but the Fine Dharma, the great master to Buddhas and Bodhisattvas, is ordained as the Sacred Object of Worship in accordance with the scripture and the spirit of Nichiren Shonin when he established this sect.
—Honmon Butsuryu Ko Koshi—805 -807
However, this was not Nissen Shonin's own discretion. He just followed Nichiren Shonin's instructions. Nichiren Shonin considered that among the sutras which were taught by Shakamuni Buddha, the Lotus Sutra is the most important sutra. Because the Lotus Sutra contains the essence of all of Shakamuni Buddha's teachings and it unified and incorporated the sutras of others in which Buddhas, Bodhisattvas and the guardian kings of heaven appear and elaborated on its teaching.
Nichiren Shonin stated in his writing "Kanjin Honzon Sho" what the Gohonzon's aspect should be.
So far as the spectacle of the Sacred Object (Myohorengekyo) is concerned, it was situated in the center of the jeweled stupa floating in the sky above the Saha world, the land of the Primordial Buddha. Inside the stupa, on both sides of the Myohorengekyo, the Buddha Sakamuni and the Buddha Prabhutaratna (Taho) were seated. The main attendants of the Buddha Sakamuni were the four bodhisattvas, led by Visistacaritra (Jyogyo), while Manjusri, Maitreya and other bodhisattvas were seated below as attendants of the four Bodhisattvas.
The great or small bodhisattvas, who had been converted by the manifestations of the Buddha or who had come from other worlds were there looking up at the above mentioned great Buddhas and Bodhisattvas like ordinary people looking up at nobles in court. The Buddhas from the ten directions were seated on the ground, not in the sky; they were showing that they were as manifestations of the eternal Buddha representing their manifested lands.
So, in the Gohonzon Mandala composed by Nichiren Shonin, the Odaimoku, Namu Myoho Renge Kyo, the Fine Dharma enlightened by the Eternal Buddha, is written in the center of the Mandala, and on the right side and left side of the Odaimoku, the names of Shakamuni Buddha and Taho Buddha, bodhisattvas and the guardian kings in heaven are written in order.
An allegory is given below for clarification.
The Odaimoku in the Gohonzon is like a large tree. Buddhas, bodhisattvas, and others are the many parts that comprise this tree like the branches and leaves. So there is no need to display the icons of them in front of the Gohonzon. To display icons of them in front of Gohonzon is like breaking off the branches and harming the tree.
Nissen Shonin, the founder of HBS noted:
Among the Three Great Secret Laws, the True Law which plants the seed, genuine cause of
Buddhahood in the minds of living beings is the Daimoku and nothing else. It is obvious that only the Daimoku is the Sacred Object to those who perform Buddhist practice in the period of the last Dharma. At the beginning of “Questions and Answers on the Object of Worship" or Honzon Mondo Sho by Nichiren Shonin, it is said the only Buddhist teacher is the Dharma and it is absolutely out of place to revere Buddha Shakyamuni as an object of worship. It is undeniable that the Odaimoku is the object of worship about which Nichiren Shonin said, `Such a sublime Sacred Object was revealed only in the primordial eight chapters of the Lotus Sutra.' In his Kanjin Honzon Sho, Nichiren Shonin shows the Altar as the Saha World in the primordial time, the Odaimoku as Namu Myoho Renge Kyo inside the stupa, and the Spectacle of the Sacred Object by the primordial Buddha and primordial bodhisattvas', and further shows the superiority of the primordial division of the Lotus Sutra to the provisional division by the fact that the primordial Buddha is in the sky above the Saha world, whereas the manifestations of the Buddha are on the earth. Nichiren Shonin says; 'the primordial Buddha Shakyamuni wrapped all these things up in the Odaimoku and permitted believers to have it as the Sacred Object. This Sacred Object is nothing but Nichiren's soul and the meritorious world moving forward in faith. The Odaimoku is the greatest mandala without precedent as the Sacred Object of Worship.'
The Gohonzon (The Object of Worship) of HBS
Nissen Shonin explaines the reason for this
Nissen Shonin, the founder of HBS noted: