The topic at hand:
At that time again, Mahāmati the Bodhisattva-Mahāsattva said this to the Blessed One: It is told by the Blessed One in the canonical text the Tathagatas of the past, present, and future are like the sands of the river Gangā. Blessed One, is this to be accepted literally? or is there another distinct meaning?
No, not literally, but the sands of the river Gangā are nondiscriminatory in themselves. Therefore
Those who regard the removers of obstruction [i. e., Buddhas] as neither destroyed nor departed for ever, like the sands of the Gangā, see the Tathagata.
Like the sands of the Gangā they are devoid of all error: they flow along the stream and are permanent, and so is the essence [or nature] of Buddhahood.