Prior to the Exodus, when the Israelites escaped the slavery of the Pharaoh of Egypt (see Who Was The Exodus Pharaoh?), the ancient way of worship was yet observed, with the firstborn son of each household inheriting the priest's office. That was changed at Sinai (see Wilderness Journey) when a hereditary priesthood from the family of Aaron was established (Exodus 28:1).
The Levites were formally set apart after the now-infamous incident with the golden calf idol that the Israelites made while Moses was away receiving The Ten Commandments from The Lord (Exodus chapter 32). The Levites did not take part in the idolatry, and actually killed 3,000 of those who were running wild, as ordered by Moses (Exodus 32:25-29).
After the incident was over, Moses said of the Levites, "Today you have ordained yourselves for the service of The Lord, each one at the cost of his son and of his brother, that he may bestow a blessing upon you this day." (Exodus 32:29). The Levites were natural allies of Moses because Moses himself was of the tribe of Levi (Exodus 2:1-2,10).
Levi had 3 sons - Gershon, Kohath, and Merari. From those branches of the family, the Levites were organized into 3 levels of service:
The Levites served at the Tabernacle from age 30 to 50 (Numbers 4:3,23,30). They were not counted for military service in the armies of Israel, but were set apart for service to God (Numbers 1:45-50, 2:33, 26:62).
Levites had custody of The Tabernacle (as illustrated above, see also What Happened To The Tabernacle?) (Numbers 1:51, 18:22-24). The Gershonites camped on the west of the Tabernacle (Numbers 3:23), the Kohathites on the south (Numbers 3:29), the Merarites on the north (Numbers 3:35), and the priests on the east (Numbers 3:38).
With their consecration to The Lord's service, the Levites were allotted no territorial inheritance of their own at the Division Of The Land; God was their inheritance (Numbers 18:20, 26:62, Deuteronomy 10:9). Once established in the Promised Land, they were supported, in the agricultural economy of the time, by the tithes of the produce of the land paid to The Lord by the other tribes.
The Levites were assigned towns to live in from the inheritance of the other tribes - forty-eight cities, thirteen of which were for the priests along with their other inhabitants (Numbers 35:2-5). Nine of these cities were in Judah, three in Naphtali, and four in each of the other tribes (Joshua chapter 21). Six of the Levitical cities were designated as Cities Of Refuge
Fact Finder: Was John The Baptist a Levite, a descendant of the priestly line of Aaron?
See also Elizabeth