In plain words
That is: at times when he is happy and at ease, sāttvic feelings of calm rise up to some extent; again, when things happen against his wish, he grows agitated, forgets his humanity and falls prey to passion to some extent; or, when he has gorged himself to a full belly, he sinks into the tamas guṇa, that is, he settles coolly into sleep. Just as these three guṇas live like this in each one of us alone, and just as there are not three bodies for these three guṇas, in the same way heaven, the mortal world and the nether world arise in man only according to the natures of the mind. This very thing: they divided it into four places, āstika, yāstika, āstika-nāstika and nāstika. ‘It is quite all right even if you are a nāstika, but you must not be an āstika-nāstika,’ they said. So never set about riding two horses at all. ‘When you do not know how to ride, it does not matter if you never mount a horse, or it is all right too to mount one horse, but riding two horses is very dangerous,’ he taught in the meaning of this śloka. All this: that this stream of the Gaṅgā is the very stream of the Ātma, the divinity within man. So a close bond has formed between the sacred Gaṅgā in Bhārata and the stainless feelings of Satya in the heart of man. So the Dharma of Bhārata is like the stream of the Gaṅgā. The form that takes on a shape eternal and true, never sullied, never made impure, never spoiled: that very form, the Dharma of Bhārata, has come down to this world in the form of the Gaṅgā. These sacred gems Śaṅkara gave are free of selfishness. How so? The stream of the Gaṅgā never sets about drinking for itself. A good fruit tree does not set about eating its fruit itself. In the same way, the noble are great souls who do not use all their powers, too, for their own sake, but give them up for the welfare of the world.