You Must Count for Yourselves
Even though, when the Temple is not standing, we cannot offer up the Omer of barley on the second day of Passover, we still commence counting the 50 days "of the Omer" from that day. The days of "counting the Omer" act as the bridge between our annual reliving of the Exodus from Egypt (on Passover) and our annual reliving of the Giving of the Torah (on Shavuot).
The Jewish people did not "earn" the Exodus; in fact, G-d had to "artificially" give them something to do in order to merit their redemption in at least some small way. Thus, G-d took the initiative in the Exodus, pulling His people out of their spiritual and physical bondage despite their unworthiness. Because they were not redeemed on their own merits, their redemption could not transform them in any way. Spiritually, their human/animal souls remained unrefined despite the experience. For this reason, the spiritual effect of the Exodus was temporary; the spiritual danger represented by Egypt still remained.
The revelation at Mount Sinai, however, was a lasting and meaningful one, which indeed transformed them, and us for all time. It was here that they received the full manifestation of their Divine souls, after internalizing the Exodus, the Splitting of the Sea, and all the incidents that occurred en route to Mount Sinai.
We undergo this same dynamic in our annual reliving of the Exodus and the Giving of the Torah. Just as G-d miraculously renews nature each spring, He re-inspires us each Passover, freeing us from the wintry, depressing bondage to the forces of physical and spiritual entropy rooted in the materialistic consciousness of our human/animal soul. However, since this quantum leap (Pesach, the Hebrew name of Passover, means "jump") is largely His doing, it cannot transform us in any lasting way. That can be accomplished only by a renewed acceptance of the Torah on Shavuot, and the way we prepare for Shavuot is through counting the Omer.
Our human/animal soul comprises both intellect and emotions. Rectifying the emotions of the human/animal soul requires arduous work, since the emotions themselves have to be recast, not only reoriented. This process therefore is more complicated, and is accomplished by the seven-week process of counting the Omer.
Our emotional makeup, including that of our human/animal souls, derives from the seven emotional attributes through which G-d created the world and continues to relate to it.
In childhood, these emotions are "one-dimensional," i.e., absolute and unmitigated. In contrast, the emotions of mature adults have been tempered by their intellect, so they are less extreme and intense. On the other hand, it is fairly easy to calm a child's emotions, since they are not as stable as those of an adult, whereas those of an adult, being more solidly grounded in the intellect, are harder to change. Thus, the process of maturation may be described as the process whereby the intellect learns how to influence the emotions.
This is the process we undergo through counting the Omer. Each week, in turn, we refine one of the seven emotions of our human/animal soul by submitting it to the guidance of the intellect.
During the seven days of each week, we add another emotional dimension to the emotion we are focusing on that week.
Each day thus presents us with a very specific and clear objective: to work on and refine one aspect of our human/animal soul's emotional makeup. Through this process, this soul matures and is ready to welcome the renewed manifestation of our Divine soul that takes place when we relive the Giving of the Torah on Shavuot.
--From Kehot's Chumash Vayikra