Chapter ten is a list, and readers who want argument find it the least rewarding part of the Gita. Read as a method rather than as content it is one of the most practically consequential chapters in the book.
Arjuna's question is specific. He does not ask what God is. He asks how he should think about God while looking at the world, and in what particular things he should contemplate him. The answer is a long series of identifications, each taking the first or best member of a class: of the shining ones the sun, of the stars the moon, of the Vedas the Sama, of the senses the mind, of mountains Meru, of bodies of water the ocean, of rivers the Ganga, of letters the first letter, of seasons the flowering spring, of weapons the thunderbolt, of the immovable the Himalaya.
The device gives an ordinary person a usable practice with no equipment. Whatever is in front of you belongs to some class of things; find the pre-eminent member of that class and you have a foothold. This is why the passage is so often used in teaching, and why so many of its identifications entered general Indian usage as ordinary figures of speech.
Two entries in the list are worth noting because they are not superlatives of the obvious kind. Among cheats, Krishna says, he is the gambling of the dishonest, and he is the rod of those who chastise. The catalogue is not confined to what is admirable. It names the concentrated form of whatever a class contains, including its capacity for harm, which is consistent with the vision that arrives in the next chapter.