According to some calculations of the 613 mitzvos (the Maharam Shi"k and others) sefiras ha'omer is the middle mitzvah of the Torah. There are 306 mitzvos before sefiras ha'omer, and 306 mitzvos after it; sefiras ha'omer is mitzvah #307, the exact middle of the 613 mitzvos.
The Barnover Rav zt’l (Reb Avraham Simchah, in his sefer Orah v'Simchah) writes that just as a center-beam holds up the entire structure, sefiras ha'omer is the foundational mitzvah of the 613 mitzvos and it holds up all the mitzvos of the Torah.
Sefiras ha'omer purifies us. As we say in the prayer after sefiras ha'omer, לספור צויתנו אתה וכו ומטומאותינו מקליפותינו לטהרנו כדי העומר ספירת, "You commanded us...to count sefiras ha'omer to purify us from our impurities..." This purity connects us to Hashem. Counting the omer is the foundation, the middle, the central beam that enables us to keep the entire Torah.
It states (Shemos 26:10), לולאת חמישים ועשית, "you shall make fifty hooks." The Chida zt’l (Lechem Min HaShamayim, Trumah, 21) quotes Rabbeinu Efraim, who says that the fifty hooks correspond to the fifty days of sefiras ha'omer. Just as the fifty hooks connected the coverings of the Mishkan, the fifty days of sefiras ha'omer connect us to our Father in heaven.
If we want a source that sefiras ha'omer purifies us, we don't have to look further than the Torah itself. It states (Vayikra 23:15), השבת ממחרת לכם וספרתם, "Count...from the day after yom tov..." The Or HaChaim Hakadosh says that וספרתם comes from the word ספיר, sapphire. לכם וספרתם means that by counting the omer you will become pure and your neshamah will shine like sapphire.
Reb Efraim Waxman Shlita, Rosh Yeshivas Me'or Yitzchak, told me that when he was a child learning in cheder, one of his melamedim was a holocaust survivor. When the children were acting up and misbehaving, he would mumble something under his breath. The children could sometimes make out a few words he said. They didn't know the meaning of the words, but they were sure he was cursing them in Hungarian.
At the end of the year, the children asked their melamed for forgiveness for causing him so much distress over the year, until he cursed them. The melamed replied, "Chas v'shalom! I never cursed you. I was saying פנטרי טרקיא קנכרי, etc. These words are Onkelos’s translation to וברקן ירקן סמקן, the precious gems of the choshen, which the kohen gadol wore."
The melamed explained, "The gems on the choshen represent the Jewish nation, and it teaches that they are precious gems before Hashem. To control my anger, I reminded myself that you are all precious children of Hashem." And as we explained, the polishing of these precious stones (of our holy neshamos) happens when we count sefiras ha'omer.
The Ben Ish Chai (שניה שנה וירא) writes, "When a person argues with his wife, children, or servants [on Fridays], he certainly thinks that he is right, and that he is justified for making this machlokes, because they did something wrong. But the truth is, someone with intelligence would understand that even if they did something wrong, it wasn't their fault. It was the Satan who tries to cause fights at this time... Therefore, everyone should understand that...he shouldn’t blame his wife, children, or maid and shouldn’t argue with them. Instead, remember this excuse, as it is true. He will remain silent, he won't fight with them, he won't get angry, and it will be good for him in this world and the next."
There are segulos that save us from the Satan, who causes fights on Fridays. The Shlah HaKadosh (שבת מסכת, 'ד אות מצוה נר) writes, "The Reishis Chachmah taught in the name of his rebbe [the Rema'k] that one should remove the cobwebs from the walls of his home on erev Shabbos... And I will reveal a secret... These cobwebs are the kelipos, which seek to destroy the shalom bayis. Therefore, we have to get them out of the house..."
The Kaf HaChaim (י"סק נ"ר) quotes this segulah and adds, "Get rid of the cobwebs on Friday before the fifth hour of the day, because from the fifth hour on begins the light of Shabbos."
Another segulah is from the Ateres Tzvi of Ziditchov zt'l: "We have a kabbalah that to banish this Satan [who seeks to start fights in the home on Fridays and Shabbos] one should put on the Shabbos tablecloth before midday."
