The weapon is needed to slay the rooster Viðofnir atop the Mímameiðr tree in order for the seeker to achieve his quest, or so replies the wise porter Fjölsviðr, the titular character of the poem.
Lævateinn is the only weapon capable of defeating the cockerel Viðofnir, as explained by Fiölsvith "the very wise" porter in the poem Fjölsvinnsmál.
Hvart ſe vapna nockvt þat er knegi Viþofnir for Hníga á heljar ſjót?“
Svipdag spake: "Now answer me, Fjolsvith, the question I ask, For now the truth would I know: What weapon can send Vithofnir to seek The house of Hel below?"
Fjolsvith spake: "Lævatein is there, that Lopt with runes Once made by the doors of death; In Lægjarn[Loki]'s chest by Sinmora lies it, And nine locks fasten it firm".
The Laeva- stem of the weapon's name is considered the genitive form of Lae-, as occurs in Loki's nickname Lægjarn, where lae means 'deceit, fraud; bane', and so forth.
[21][d] Henry Adams Bellows glossed Lævateinn as meaning 'wounding wand', but rejected identification with the mistilteinn or "mistletoe with which Baldr was killed".
[4] To complicate matters, the argument is also made by e.g. Lee M. Hollander that although Lævateinn is literally renderable as a "Wand-of-Destruction", it is etymologically considered to be a kenning for a sword.