They were taken captive to Babylon because of their unfaithfulness

1 Chronicles 9:1-44

All Israel was listed in the genealogies recorded in the book of the kings of Israel and Judah. They were taken captive to Babylon because of their unfaithfulness.

Now the first to resettle on their own property in their own towns were some Israelites, priests, Levites and temple servants.

Altogether, those chosen to be gatekeepers at the thresholds numbered 212. They were registered by genealogy in their villages. The gatekeepers had been assigned to their positions of trust by David and Samuel the seer. They and their descendants were in charge of guarding the gates of the house of the Lord—the house called the tent of meeting. 

Some of them were in charge of the articles used in the temple service; they counted them when they were brought in and when they were taken out.

Those who were musicians, heads of Levite families, stayed in the rooms of the temple and were exempt from other duties because they were responsible for the work day and night.

All these were heads of Levite families, chiefs as listed in their genealogy, and they lived in Jerusalem.

Why?

The Levites were assigned as the servants of the Lord, serving in the Temple of the Lord.

No matter how great Jerusalem was, the Israelites were taken captive to Babylon because of their unfaithfulness to the Lord.

How?

Serve the Lord has many positions and many jobs. Each one plays an important role.