When we "feel" our pure Self

 We are still we, and the mountain is still the mountain, but we and the mountain are two sides of one and the same experience, which is the one and only reality at that moment.

While we are resting in that state, and "sensing" this Witness as a great expanse, if we then look at, say, a mountain, we might begin to notice that the sensation of the Witness and the sensation of the mountain are the same sensation. When we "feel" our pure Self and we "feel" the mountain, they are absolutely the same feeling.