Numbers can have some significant symbolic meanings in the Bible. And it appears that the number 12 represents a balanced and complete arrangement according to divine standards.
Jacob had 12 sons, who became the foundations of the 12 tribes of Israel. Further, these are 12 tribes of the sons of spiritual Israel, each tribe consisting of 12,000 members of which is quoted in Rev. 7:4-8.
Interestingly, 12 apostles were also chosen, who form the secondary foundations of the New Jerusalem, built upon Jesus Christ. (Mt 10:2-4; Re 21:14)
In this sense, multiples of 12 (or 12 + 12) are also mentioned. David established 24 divisions of the priesthood to serve by turn in the temple later built by Solomon. (1 Ch. 24:1-18)
This 12 + 12 combination is also used in identifying the 24 elders who were seated round about God's throne in white outer garments and who were wearing crowns. (Re 4:4)
So learning about this usage of the number 12 throughout the Bible (especially when considering Rev. 7:4-8...12 times 12,000 = 144,000) can help us better understand the numerical significance behind the divine representation of a balanced & complete arrangement.
For more, see:
Twelve - Links to Information (INDEX; Watchtower Online Library)