Samuel was born into the tribe of Ephriam (I Samuel 1:1). His mother was childless, and during a visit to the tabernacle, she made a vow. "O LORD of hosts, if You will indeed look on the affliction of Your maidservant and remember me, and not forget Your maidservant, but will give Your maidservant a male child, then I will give him to the LORD all the days of his life, and no razor shall come upon his head" (I Samuel 1:11).

The vow is particularly noteable because under the Old Law, first born children were considered dedicated to God. Before the Levites were picked to serve in the tabernacle and later in the temple, first born children were selected to serve. "Now behold, I Myself have taken the Levites from among the children of Israel instead of every firstborn who opens the womb among the children of Israel. Therefore the Levites shall be Mine, because all the firstborn are Mine. On the day that I struck all the firstborn in the land of Egypt, I sanctified to Myself all the firstborn in Israel, both man and beast. They shall be Mine: I am the LORD" (Numbers 3:12-13). Because of the replacement, God had the Israelites redeem (buy back) their first born. "Everything that first opens the womb of all flesh, which they bring to the LORD, whether man or beast, shall be yours; nevertheless the firstborn of man you shall surely redeem, and the firstborn of unclean animals you shall redeem" (Numbers 18:15). However, a person was not allowed to reuse a redeemed item for another vow. If it was dedicated to God a second time, it whole belonged to God. All rights to the devoted person, animal, or thing is completely terminated. "Nevertheless no devoted offering that a man may devote to the LORD of all that he has, both man and beast, or the field of his possession, shall be sold or redeemed; every devoted offering is most holy to the LORD" (Leviticus 27:28).

Since Hannah devoted her first born to the Lord, but he was already devoted by God's law and was to be redeemed, Hannah was effectively giving up all rights to her son. He then became a possession of the Levites. In other words, though born of the tribe of Ephriam, because of his mother's vow, he became a member of the Levites. Since Eli, a descendant of Aaron, took him into his household, Samuel became a member of Aaron's lineage. He was now not only a Levite, but also a priest.