I feel that three quarters of the first shloka of the Isha Upanishad is enough for someone to see what I have seen.
Shlokas are usually written in two lines of text. Here is the first shloka:
Line 1: first half: Ishavasyamidam sarvam
There are many ways to understand this. I understand this to mean “Isha is the stuff out of which is made everything here and everywhere.”
Line 1: second half: yatkincha jagatyam jagat
This is interpreted in two ways. One says: everything in this universe is in constant motion. I interpret it thus: the universe is the term used to denote everything which is in constant motion. Or: that which is in constant motion is termed the universe. In other words, I see that the very definition of “jagat” or universe is by its characteristic of ceaseless motion.
Line 2: first half: tena tyaktena bhunjitha
“Let go and rejoice.” There are many other choices of words, I guess, but this is how I’ve internalised it from my master. Works for me.
I’ll let the second half of the second line be.
How they fit together
The first half of the first line tells me that Isha is everywhere and is everything. The second half of that line tells me the nature of the universe. By its fundamental definition itself, its ever-changing nature is asserted.
The second line pulls these two together and tells me, as plain as detailed instructions to a clerk, what I need to do. I need to let go and rejoice.
By this time in the shloka, I have been told that the Absolute Reality is everything, and the nature of the material universe is ceaseless change. This means that I cannot hold on to anything in the material universe — everything will emerge and disappear, everything I hold onto will slip from my grasp, and I too am going to undergo ceaseless rise and fall. At the same time, there is nothing to hold on to, since everything is the same internally — everything is the Absolute Reality. No part of the universe is more preferable or less, than any other.
Therefore, not only is holding on impossible, I am being told not to hold on. I am being told, let go and rejoice. This letting go is the most difficult thing to grasp, partly because it is not something to grasp — it is a switch to throw. Throw the switch. Do not analyse it or understand it. All that analysis is grasping. Let go even the need to understand the instruction of letting go. Just let go, and rejoice.
The rejoicing comes from the fact that once everything is let go of, there is literally nothing else to do, nothing to worry about, nothing to achieve, nowhere to reach. Therefore, the rejoicing is the natural side-effect, the only residual effect, of letting go. And once you reach this point, you will understand everything I have understood.