The mandala form originated in India and evolved in Tibet. Tibetan mandalas have four (or multiples of four) sides. The outer corners are usually protectors of the Buddha wisdom within. Tibetans use images instead of words to enable those who can't read to feel reverence. 

Mandalas are splendid religious art. If you see one in a museum, lean close, you may catch a whiff of the incense offered to it.  It may have the fragrance of hundreds of years of devotion. Rich. 

The mandala's center is the central Buddha. This Buddha holds his/her body in different ways (mudras), to convey meaning. For instance, you may have seen the Tantric Mandala depicting a black man in sexual union with a white woman, or a white man in sexual union with a black woman. 

To the western eye this mandala appears to be about sex or race. It is neither. It is the fusion of opposites. The Mystic Embrace. The gate of emancipation. Clear Light. The denial of duality. Ku. To this consciousness, sex and race are illusions. 

Many of the characters on our Gohonzon have mandalas of their own. Each are Laws, Buddhas and vast experiential realms. 

In the Lotus Sutra, Taho and Shakyamuni are seated in the treasure tower, facing each other and speaking the Lotus Sutra in unison. 

On the Gohonzon they face each other and "Namu Myoho Renge Kyo" indicating the fusion of objective reality (Taho) and subjective wisdom (Shakyamuni). 

"Taho represents all phenomena and Shakyamuni, the true entity.  The two Buddhas also indicate the two principles of object (kyo) and subject (chi), or reality and wisdom.  Taho Buddha signifies the object and Shakyamuni the subject."  

—Major Writings, Vol. 2, p. 229, "Earthly Desires are Enlightenment"

Nichiren wrote: "You must never seek any of Shakyamuni's teachings or the Buddhas and bodhisattvas of the universe outside yourself."  —Major Writings, Vol. 1, p. 4, "On Attaining Buddhahood" 

He also wrote: 
"Explaining the wonder of life is the prime objective of all the sutras, termed the eighty-four thousand teachings. These doctrines all exist in one's life.  Accordingly, the eighty-four thousand teachings are the diary of one's life. We hold and embrace the eighty-four thousand teachings in our lives. To suppose that the Buddha, the Law and the pure land of Eagle Peak exist apart from one's life and to seek them outside is a delusion."  

—Gosho Zenshu, pp. 563-64, "The Ultimate Teaching 

Affirmed by All Buddhas of Past, Present and Future"

And: 
"Shakyamuni, Taho, and all the other Buddhas in the ten directions represent the world of Buddhahood within ourselves. By searching them out within us, we can receive the benefits of Shakyamuni, Taho, and all other Buddhas."  

—Major Writings, Vol. 1, p. 64, "The True Object of Worship