यस्माद्विष्टमिदं सर्वं तस्य शक्त्या महात्मनः ।तस्माद्विष्णुरिति ख्यातो विशेर्धातोः प्रवेशनात् ॥
In plain words
Everything here is pervaded by the power of that vast Self — and that is why he is called Viṣṇu. The name comes from the root viś, which means to enter, to go all the way in.
Close to the Sanskrit
Because all this is pervaded by the power of that great-souled one, therefore he is known as 'Viṣṇu', from the root viś, in the sense of entering.