Namu Amidabutsu (a Single, Sincere Call upon the Name of Amida) (南無阿弥陀仏)

The 'Namu' of Namu amidabutsu is a transcription of namo (Sanskrit), meaning 'I'm becoming a believer' and 'amidabutsu' employs amita (Sanskrit) is abbreviated from 'amitaayus (Great Buddha with infinite longevity)' and 'amitaabha (Great Buddha with infinite light),' meaning 'immeasurable' in Sanskrit. Given that the description in "The Ippen hijiri-e (Painting of St. Ippen)" states 'Namo amitafu,' it seems to have been pronounced 'Namo amidabu' during the Kamakura period.

Amida Buddha made the Original Vow to lead those who honor its own myogo (name of the Buddha) to the Pure Land, and completed all the merits for going to the heaven, which mankind must pursue, on their behalf, as included in the myogo (Namu amidabutsu) for eko (Buddhist thoughts of outgoing and returning) for mankind.

Shandao clarified the interpretation (Interpretation of the Six Characters) in six letters combining two letters of 'Namu (南無)' and four letters of 'amidabutsu (阿弥陀仏).'
Accordingly, Shinran said that because 'Namu amidabutsu' is the cause for mankind to go to the Pure Land, they must listen to and believe the origin of the myogo, 'the calling of the Buddha, saying, trust it and it will save you.'
Shinran set the myogo as the honzon (principal image of Buddha), and created six-, nine- and ten-letter myogo.
Additionally, because Shinran pronounced '南無' as 'Namo,' the Hongan-ji school of the Jodo Shinshu (True Pure Land) sect customarily calls it 'Namo amidabutsu.'

Gangyo-gusoku (fulfillment of wish and practice)

It is an interpretation shown by Interpretation of the Six Characters of Shandao, as mentioned above. "Gan" refers to the wishes of those among mankind who believe 'Namu' and Amida Buddha. "Gyo" refers to the ascetic practices of Amida Buddha for the salvation of mankind. It is a theory that since they have both become 'Namu amidabutsu,' the 'vow to attain enlightenment' and 'practices of Bodhisattva,' which Bodhisattva must pursue, are contained in the myogo.

Kiho-ittai (unity of faith and power)

It is a term that shows the doctrine of Tariki Hongan (salvation through the benevolence of Buddha), which Yuzu Nenbutsu (reciting the name of Amida Buddha), the Nishiyama school of the Jodo (Pure Land) Sect, the Jodo Shinshu sect and the Jishu sect all preach. "Ki" refers to the faith of mankind (Namu). "Ho" refers to Honganriki (power of the original vow) of Amida Buddha, who saves the mankind (amidabutsu).
It is an interpretation that Ki of mankind and Ho of Amida Buddha have inseparably united and become 'Namu amidabutsu.'

[Original Japanese]