Here we are, smack dab in the middle of Sefira (in fact, I've just been counting the days waiting to say this Dvar Torah!). Our sedra actually devotes a full section, in its discussion of the moadim (festivals), to the Omer and its rituals.
But what is quite strange is that, rather than discuss the Omer in the section dealing with Pesach - where you would think it naturally belongs - the Torah starts a whole new paragraph ("Speak to B'nei Yisrael...." etc.) on the subject of the Omer. Why the separate section?
Rabbi Soloveitchik, z.t.l., offers a fantastic insight. Pesach is a time of unlimited joy and achievement. Anything we truly desire to attain is attainable on Pesach. The Exodus from Egypt and our liberation from slavery to become the greatest nation on Earth are among the many miracles of Nissan, and attest to the nisim and niflaot - the wonders and miracles - possible this month.
A deeper understanding of why the Torah says that we begin counting the Omer "mi-macharat Ha-Shabbat."


A deeper understanding of why the Torah says that we begin counting the Omer "mi-macharat Ha-Shabbat."

But Sefira, counting, is by its very definition imperfect and lacking. The fact that we are building up towards something indicates that we have not yet attained it; we're still missing something and apparently have a long way to go until we achieve it.
Says the Rav, this is the paradox of Man. On the one hand, Man is G-d's greatest creation, king of all other creatures, virtually limitless in his ability to create new worlds: "What Man can perceive, Man can achieve." Yet, at the same time, Man must set certain limits for himself and recognize his own mortality. He must never be fully satisfied with where he is today, but rather must seek to grow in holiness and G-dliness, and come closer to HaShem. Each day is an achievement, a plateau - but tomorrow we must scale even higher. And so, the greatest praise we can bestow upon a scholar is to call him a talmid chacham, a student seeking even greater wisdom.
Note that the word omer is used not only in connection to Sefira, but also in relation to the Mahn that fell from Heaven. Mahn is a metaphor for money (mahn-ee?). We can achieve amazing things with wealth, but it, too, has its limits. And so G-d commands us to stop "collecting" it when Shabbat comes.
Now, perhaps, we have a deeper understanding of why the Torah says that we begin counting the Omer"mi-macharat Ha-Shabbat," on the day following the Shabbat (which chazal interpret in this case as referring to the first day of Passover).
Only when Shabbat was over, could the people collect the Mahn; and when the first chag of Pesach concludes, they brought the Omer. The lesson: Man must strive for his daily bread, but he must also know that it is spiritual richness - as represented by Shabbat and Pesach - which is the true pot of gold at the end of the rainbow.