लेलिह्यसे ग्रसमानः समन्ता ल्लोकान्समग्रान्वदनैर्ज्वलद्भिः।तेजोभिरापूर्य जगत्समग्रं भासस्तवोग्राः प्रतपन्ति विष्णो॥
lelihyase grasamānaḥ samantāllokān samagrān vadanair jvaladbhiḥtejobhir āpūrya jagat samagraṃbhāsas tavogrāḥ pratapanti viṣṇo
Word by word
The verse says
You are licking up all the worlds on every side with your flaming mouths, swallowing them. Your fierce rays fill the whole world with light and scorch it, Viṣṇu.
In plain words
The last line puts the two halves together: the same rays fill the world and burn it.
Not two actions. One.
Whatever is doing this is not switching between creating and destroying. It is doing one thing, and both words describe it.
Where you've felt this · at work
Your neighbour hangs the washing out at eight and brings it in dry by eleven. By two in the afternoon the same sun has cracked the yard open and nobody goes outside. He is not dealing with two suns. There is no setting on it.
Going deeper
One process described by two words is the idea this verse leaves the reader with before the explanation arrives.
Filling the world with light and scorching it are the same action, performed by the same thing, at the same moment. Nothing switches. There is no mood in which it stops. Arjuna has been looking for an intention behind what he is seeing and this is the closest the description comes to telling him there is not one of the kind he is looking for.
Chapter 9 said the same thing more calmly: I am what does not die, and the ending too, and I give the heat and hold back the rain.
The difference is that there it was a doctrine and here it is being watched. Which is why the next verse is a question rather than another description — he has run out of ways to describe it, and he needs to know what it is.