“Appoint judges and policemen in all your gates which G-d your G-d gives you, according to your tribes, that they may judge the people equitably.”

Although it is not evident in English, the imperative “appoint” as well as the pronouns “your” and “you” are in the singular.
Sefer HaLikutim, parashat Shoftim

Why is this commandment phrased in the singular, rather than in the plural?

We heard in the name of the esteemed Rabbi Chaim Vital, of righteous memory, that this is so in order to indicate that every individual Jew has several “gates.” These are: the gates of sight, the eyes; the gates of hearing, the ears; the gate of speech, the mouth; the gate of smell, the nose; the gate of touch, the hands and feet.

Just the gate of a domain is a passageway through which one enters and exits, the “gates” of the person are his sense organs, through which stimuli enter his mind and he reacts to the outside world. The skin—here represented by the hands and feet, its principle loci of action, is in fact considered an “organ” in many biological contexts, no less than the other organs mentioned here.

Thus, a person must position “judges” and “policemen” at each of these “gates,” in order to protect himself from looking at women forbidden to him, listening to untoward matters, speaking in a foul or malicious manner, smelling the perfume of a woman forbidden to him, touching such a woman or walking to commit a sexual sin, or walking to theatres or circuses. This is why “your gates” is phrased in the singular, in order to indicate the above.

When a person guards his “gates” from sin, it is said of him, “Open up, O gates, that a righteous nation may enter,” measure for measure. Furthermore, the 310 worlds destined for every righteous person will open their gates for him, for every world has its entrance gate.

The final section of the Mishnah begins: “Rabbi Yehoshua ben Levi said: The Holy One, blessed be He, will in the future bequeath every righteous individual three hundred and ten worlds, as it is written: ‘To bequeath substance to My beloved, and I will fill their storehouses.’” The numerical value of the word for “substance” (yesh, yud-shin) is 310.

Know as well, that on the path from here to heaven there are all sorts of accusing angels and angels of destruction, and there are a number of gates to each of the seven heavens, each of which is guarded. When the soul ascends it is inspected. If it is worthy, the gates are opened for it and it is permitted to enter. If it is not, it is pushed outside, the gates are closed before it and it is not allowed to enter. For this reason, every intelligent person should take this teaching to heart while he is still alive and control and guard his “gates,” as we said above. He will then merit to have the gates of righteousness opened before him, as we have said.

The “accusing angels” and “angels of destruction” are the corresponding elements to “judges and policemen” on the side of evil. The accusing angels tally off the individuals sins, which were brought about by not properly guarding his “gates,” and the “angels of destruction” cause the ascending soul to suffer accordingly.

The seven heavens are listed in the Talmud:

7 Aravot “darkness”

6 Machon “residence”

5 Ma’on “habitation”

4 Zevul “habitation”

3 Shechakim “dust”

2 Rakia “firmament”

1 Vilon “curtain”