At the end of the Book of Job, God dramatically appears to Job out of the whirlwind and says: 'Who is this that darkeneth counsel by words without knowledge? Gird up now thy loins like a man; for I will demand of thee, and declare thou unto Me. Where wast thou when I laid the foundations of the earth? Declare, if thou hast the understanding' (Job 37, 2-4).
The Midrash, though, says that God simply showed Job a Sukkah.
Why, asked Reb Ahron, a Sukkah? As we all know, a kosher Sukkah requires two full walls and a bit of a third wall. This, on the face of it, is odd because anyone can tell you that a real building requires four walls. So why should a sukkah require only 2.1? The truth is, though, that the Sukkah really has four walls. The remaining walls exist, in our imagination. The Halakhah is that one must use one's imagination and 'see' the remaining walls.
The same is true of our relationship with our departed loved ones. They are not physically here. However, Halakhah requires us to use our imaginations and to continue our relationship with them based upon what we know they might say or think or feel. That ongoing relationship is very real and very tangible, just like the ostensibly 'missing' walls of the sukkah, which really exist.
As we approached the steps leading down to the Kotel, I remember my eyes welled up with tears. 'You know, David,' I told him, 'this is the first time I've been reaaly consoled since my father died. עקיבא ניחמתנו, עקיבא ניחמתנו!'
And so, ידיד נפשי , that is exactly the way that I keep up our friendship: in my imagination, in the best tradition of בית בריסק.
[Note: I believe that Rav Ahron was referring to Yalqut Shimoni, Iyyov, 927 s.v. יכרו.]