It says that the number of positive commandments ["thou shalts"], 248, corresponds to the number of limbs in the human body, and that the 375 negative commandments ["thou shalt nots"] correspond to the number of tissues. When an individual transgresses, he or she harms the corresponding part of the soul; when fulfilling a commandment, a person repairs the part in the soul corresponding to the part in the body.
Our Sages, of blessed memory, did, indeed, ask: How is it possible for a person to fulfill all 248 positive commandments, since there are some that cannot be fulfilled, such as levirate marriage and the like? And there are commandments that do not apply to all People of Israel but only to Cohanim (priests by descent), such as the blessing of Cohanim and the like; there are also commandments that apply only to kings, such as, "Neither shall he multiply wives to himself".
They explained that you may consider that through unity – when the people of Israel are unified in a single society and have love for one another – each and every person fulfilling a commandment is considered as though he or she had fulfilled them all - as it says, "Moses commanded the Torah to us". Should you ask, "How can a person fulfill all 613 commandments?" it says, "a heritage to the community of Jacob". Meaning, like a heritage, it is to be fulfilled by all, by the community of Jacob, and by being as a single community - in a united society.