Who was Levi?
Levi was Jacob's third son by Leah, = joined, expressing her trust; "now will my husband be joined unto me, because I have borne him three sons" (Gen. 29:34).
Levi joined Simeon in avenging their own full sister Dinah's wrong by treacherously slaying the Shechemites, and so incurred Jacob's curse. They made circumcision, which God gave as a pledge of His holy covenant, the instrument of hypocrisy and bloody revenge. Jacob's moral weakness, in reproaching his sons not with the treacherous murder but with exposing him to danger ("ye have troubled me to make me to stink among the inhabitants of the land"), is faithfully delineated (Gen. 34).
On his death bed he took a less selfish and juster view of their deed (Gen. 49:5-7): "Simeon and Levi are brethren" in character as in birth, "instruments of wickedness are their swords (Hebrew). O my soul, come not thou into their secret" (deliberative council), renounce all fellowship with their act; "mine honour" (glory, my spirit, which is man's glory, the center of his personality framed in God's image);" for in their anger they slew a man and in their wantonness (Hebrew) houghed an ox."
In Gen. 34:28 it is merely said "they took their oxen." Gen. 49 brings out the additional fact that in cruel revenge they wantonly severed the hind foot tendons of the Shechemites' oxen. Simeon, as the one detained in Egypt, by Joseph, was probably the foremost of Levi's sons in the cruel attack on Rachel's son, and Levi probably joined him, though the spite began with the base born sons of Bilhah and Zilpah.
The discipline made the sons, once so unfeeling towards Joseph, to become self-sacrificing for Benjamin. As the two joined in crime, retributively they should be "divided and scattered" in Israel. Levi received no land inheritance but cities scattered through Israel (Josh. 21:1-40), and depended on tithes paid by the other tribes.
The curse became subsequently a blessing to the nation by Levi's separation to divine service. But Jacob does not intimate this, a proof of the genuineness of his blessing as recorded in Genesis. Moses subsequently speaks in very different language of Levi (Deut. 33:8 ff), as was appropriate after Levi's accession to the priestly honour: "let Thy Right (thummim) and Thy Light (urim) be with Thy holy one (Levi, representing the whole tribe.
The Urim and Thummim worn on the high priest's breastplate were the pledge that Jehovah would always give His people `light' to defend His `right'; they should be given to Levi because he had defended Jehovah's right), whom Thou didst prove at Massah (Exo. 17:1-7, by the people's murmuring against Moses, Levi's representative, for water at the outset of the 40 years' wanderings) and with whom Thou didst strive at ... Meribah" (Num. 20:1-13, at Kadesh, at the close of 40 years, the two comprehending the whole intermediate period). Jehovah "proved" Levi, and by the people's strivings "strove with" Levi (represented by Moses and Aaron.)
Levi proved himself in the main (for Moses' failure, Num. 20, and the Levite Korah's rebellion, Num. 16, are graciously ignored) to be Jehovah's holy one. Moses and Aaron's faithfulness, the Levites' drawing their swords against their Israelite brethren as God's avengers of the idolatry of the golden calf (Exo. 32:26-29), "slaying every man his brother ... companion ... neighbour ... son," where God's honour was at stake (Mt. 10:37; 19:29; Luke 14:26), and Phinehas' zeal against the idolaters and fornicators with the Moabite women (Num. 25:11), gained God's approval and the choice of Levi as the priestly tribe (Deut. 33:9-11).
"Who said unto his father and to his mother, I have not seen him, neither did he acknowledge his brethren ... They shall teach Jacob Thy judgments and Israel Thy law (Lev. 10:11), they shall present incense before Thee (in the holy place) and whole burnt offering upon Thine altar (in the court). Bless, Lord, his substance (rather his power) and accept the work of his hands. Smite through the lions (Ps. 69:23, the strength) of them that rise against Him," etc.; i.e., give him power for discharging duty, accept his service, and make his adversaries powerless. Levi died at the age of 137 (Exo. 6:16).
IBSE, "Isaac" (in the public domain) with minor edits.