I don't think that was stated or hinted at by Hago..
I thought it was to help Indra's descendants & Indra not go down the wrong path with the power of their eyes but to connect people with them instead like Ashura..
I think after Hago gave Ashura leadership of the clan & Ninshuu he came up with a written tablet for Indra..
Remember he seen a different way with Ashura through connecting with others & Indra only wanted to be alone after losing the clan power, leadership of Ninshuu..
The tablet was a means of connecting the brothers & all who would wield chakra through training.. IMO
I thought it was to help Indra's descendants & Indra not go down the wrong path with the power of their eyes but to connect people with them instead like Ashura..
I think after Hago gave Ashura leadership of the clan & Ninshuu he came up with a written tablet for Indra..
Remember he seen a different way with Ashura through connecting with others & Indra only wanted to be alone after losing the clan power, leadership of Ninshuu..
The tablet was a means of connecting the brothers & all who would wield chakra through training.. IMO