四明十義書 1.119

1.119

蓋由彼文正顯佛性遍義，以佛約有情說，故多明色即於心。故知若信諸色即心，則成無情有於佛性義也。

This is entirely because that text directly reveals the meaning of the omnipresence of Buddha-nature; because the Buddha is spoken of in relation to sentient beings, it mostly clarifies that form is identical to mind. Thus we know that if one has faith that all forms are identical to mind, then the doctrine that insentient things have Buddha-nature is established.