Until the sun be hot - The meaning of this is, the gates were not to be opened before sunrise, and always shut at sunset. This is the custom to the present day in many of the cities of the East if a traveler arrives after sunset, he finds the gates shut; and on no consideration will they open them till the next morning, so that those who come late are obliged to lodge in the plain, or under the walls.

Every one - over against his house - Each was obliged to guard that part of the wall that was opposite to his own dwelling.

Let not the gates (This is, the gates were not to be opened till sun-rise, and to be shut at sun-set; which is still the custom in many cities of the East. If a traveller arrives after sun-set, he finds the gates shut, and on no consideration will they open them till morning.)

Nehemiah 13:19 And it came to pass, that when the gates of Jerusalem began to be dark before the sabbath, I commanded that the gates should be shut...

Psalm 127:1 Except the LORD build the house, they labor in vain that build it: except the LORD keep the city, the watchman wakes but in vain.

Matthew 10:16 Behold, I send you forth as sheep in the middle of wolves: be you therefore wise as serpents, and harmless as doves.

every one to be

Nehemiah 3:23,28-30 After him repaired Benjamin and Hashub over against their house...

Influences that Gave Rise to the Priestly Laws and Histories
[Sidenote: Influences in the exile that produced written ceremonial laws] The Babylonian exile gave a great opportunity and incentive to the further development of written law. While the temple stood, the ceremonial rites and customs received constant illustration, and were transmitted directly from father to son in the priestly families. Hence, there was little need of writing them down. But when most of the priests were carried captive to Babylonia, as in 597 B.C., and ten years later the temple …
Charles Foster Kent—The Origin & Permanent Value of the Old Testament