The number "twelve" is a symbol of the fullness of the number of people who do the Will of God.  It is also the number of months in a year and hours in a day.

The twelve sons of Jacob became the Patriarchs, the progenitors, the physical and spiritual progenitors of the twelve "Tribes of Israel," a generation of righteous men, spiritually united by a firm faith in the Truth of Jehovah God.

The number twelve corresponds to the number of the twelve disciples of the Apostles of Jesus Christ, who expressed in completeness and accuracy the Sayings, the Teachings of Christ in the Word of the Gospel.