In all, there were 212 gatekeepers in those days, and they were listed according to the genealogies in their villages. David and Samuel the seer had appointed their ancestors because they were reliable men. 

1 Chronicles 9:22

This describes the re-institution of the organization of the temple work and workers in the early days of the second temple. They were anxious to organize things in the same manner as King David did originally.

They were ready to be serious about the Lord’s law.

Lived in the chambers of The Temple near the Priests

1. Opening the doors in the mornings and closing them at night.
2. Keeping off the unclean and the things that were forbidden by the law.
3. Directing and introducing those that came to worship.

A gatekeeper was in charge of who entered and exited The Temple.

A gatekeeper had to be trustworthy 

A gatekeeper had to be alert at all times;  he could bring ruin to everyone.

Don’t you realize that your body is the temple of the Holy Spirit, who lives in you and was given to you by God? You do not belong to yourself.
1 Corinthians 6:19

How do we secure the gate to our Temple?

• Open the doors in the morning and close them at night.
  And rising very early in the morning, while it was still dark, he departed and went out to a desolate place, and there he prayed.
  Mark 1:35 (ESV)
• Keep the unclean and the things that were forbidden out.
  Get rid of all bitterness, rage, anger, harsh words, and slander, as well as all types of evil behavior.
  Ephesians 4:31
• Direct and introduce worship.
  For God is Spirit, so those who worship him must worship in spirit and in truth.
  John 4:24

Such a small percentage of people returned.

The leaders of the people were living in Jerusalem, the holy city. A tenth of the people from the other towns of Judah and Benjamin were chosen by sacred lots to live there, too, while the rest stayed where they were.
Nehemiah 11:2

Guard my gates.