Verse 2.23 & 2.24

Here is where Krishna explains

Soul cannot be cut
Soul cannot be burnt by fire
Soul cannot be wetted by water &
Soul cannot be dried by air

He is explaining with direct connection to the elements ( Earth, Fire, Water & Air)
Gross to subtle

Earth is the Grossest
& Space/Ether/is the subtlest

Explaining gross & subtle to children is sometimes challenging.
Try doing with the 5 elements
1. Earth - we know, feel, touch, see, hold, cut - the grossest of all!
2. Water - we know, feel, touch, see, hold, but cannot cut - going towards subtle!!
3. Air - we know, feel, touch, hold, but cannot see or cut
4. Fire - we know, feel, see, touch, but cannot hold or cut
5. Space - we just know - out of reach of our 5 senses....most subtle!!!!

And Soul is surely as subtle as it can be