Eihwaz is the Rune of the World Tree Yggdrasil.
Anglo-Saxon Rune Poem
Eoh byþ utan unsmeþe treow,
heard hrusan fæst, hyrde fyres,
wyrtrumun underwreþyd, wyn on eþle.
The yew outside is a rough-barked tree,
But strong and firm, guard of fires,
By deep roots upheld, joy to the home.
Norwegian Rune Poem
Ýr er vetrgroenstr viða;
vænt er, er brennr, at sviða.
Yew is the greenest of trees in winter;
when it burns, it sputters.
Icelandic Rune Poem
Ýr er bendr bogi
ok brotgjarnt járn
ok fífu fárbauti.
Yew is bent bow
and brittle iron
and Farbauti of the arrow.
The Rune Poems dealing with Eihwaz are difficult to decipher but there are a few concepts that can be discerned. It is a Rune of strength, power and extreme vitality. English longbows made from yew basically ended the age of the iron clad knights at the battles of Crécy and Agincourt as they could penetrate plate armor, at least the cheaper models worn by about 90 % of the fighters at the time. The deep roots point at its connection to the past, which was of great importance to the Germanic peoples as Ancestor worship was one of the central pillars of their spiritual practice.
Many hints in the Eddas suggest that the world tree Yggdrasil was probably a yew tree and so in a magical context this Rune can be used to travel the world tree and the many worlds it contains. It is also very helpful in order to discover our roots, not just our genetic ones but also those that formed our current personality. It can be a great help in finding the roots of a problem or an unwanted behavior and can at the same time invest us with the necessary energy and vitality to confront and adjust it.