Tishrei is the month of judgment, the month of Rosh haShana, Yom Kippur, y'mei hadin. The name of the month begins with tuf-shin-reish, a backwards rendition of the aleph-beis. Din entails Hashem holding back until we prove ourselves worthy and pass muster.
The month we enter tomorrow is Av, aleph-beis, the first two letter in their proper order. Av is the month characterized most by Hashem's giving of himself, his midas hachessed.
Because Av is so filled with potential for chessed, the forces of destruction are strongest as well, because every force of kedusha is counterbalanced by the potential to squander that goodness and destroy it. However, even amid destruction, chessed is still there, below the surface. "Mizmor l'Assaf" -- kinah l'Assaf m'bayei leih?! The gemara answers that the title mizmor is appropriate for a psalm describing destruction because the destruction of the Mikdash was itself as act of chessed, as Hashem vented his anger on stones and wood instead of further punishing Klal Yisrael. Chessed sometimes has to be wrapped up in din to make its way into the world, but it still gets here.
Rosh Chodesh Av is the yahrtzeit of Aharon haKohen. Maharal explains that the letters of Aharon's name, (aleph) - hey-reish-nun, are the middle letters of the units of 1's (hey), tens (nun), and hundreds (reish) in the aleph-beis. Aharon is pnimiyus -- just as these letters are the innermost ones of their respective units, Aharon's personality had inner depths that could not be seen on the outside. Aharon taught us to not be fooled or swayed by the way things appear on the surface -- what appears to be a kinah could really be a mizmor. Aharon was the rodef shalom who forced people to look below superficial differences and find a deeper unity that could draw them together.
The passing of Aharon represents the removal of our sensitivity to that deepest level of pnimiyus. Unfortunately we know too well about kinos, both of past and present tragedies. We have no sense of "Mizmor l'Assaf," we do not feel justice or goodness in tragedy, even below the surface. We see Av as a month of aveilus; we have lost any sense of its character as the month of chessed, the month of ahavas shalom, the midah which Aharon epitomized. We as a people are splintered by superficial divisions and have lost any sense of the common core below the surface that unites us.
We can only hope for the day when that sense of pnimiyus will return and Av's true character will reveal itself.