What is the "All"

"Monks, I will teach you the All. Listen & pay close attention. I will speak."

"As you say, lord," the monks responded.

The Blessed One said, "What is the All? Simply the eye & forms, ear & sounds, nose & aromas, tongue & flavors, body & tactile sensations, intellect & ideas. This, monks, is called the All. Anyone who would say, 'Repudiating this All, I will describe another,' if questioned on what exactly might be the grounds for his statement, would be unable to explain, and furthermore, would be put to grief. Why? Because it lies beyond range."

http://www.accesstoinsight.org/tipitaka/sn/sn35/sn35.023.than.html

We experience our “total reality” though this sensory apparatus. There are many other things happening outside our “world,” which is the real physical world. But as far as Buddha was concerned his focus was ONLY on our immediate “sensory world” which is literally right in front of our own eyes.

This why I he called this the "All".

We do develop insight (vipassana) by examining the true nature of this "All". This is the contemplation of the three characteristics (impermanence, suffering and non-self) of the "All".