Hagalaz is the Rune that destroys existing patterns so something new can grow.
Anglo-Saxon Rune Poem
Hægl byþ hwitust corna;
hwyrft hit of heofones lyfte,
wealcaþ hit windes scura;
weorþeþ hit to wætere syððan.
Hail is the whitest of grains,
it comes from high in heaven
showers of wind hurl it,
then it turns to water.
Norwegian Rune Poem
Hagall er kaldastr korna;
Kristr skóp hæimenn forna.
Hail is the coldest of grains;
Christ shaped the world in ancient times.
Icelandic Rune Poem
Hagall er kaldakorn
ok krapadrífa
ok snáka sótt.
Hail is a cold grain,
and a shower of sleet,
and the sickness of snakes.
Hail was a very dangerous event at the time that these poems were composed. A hailstorm at the wrong time could destroy or severely damage your crops and the following harvest. At a time when there was no global trade net, that usually meant a lot of fasting during the coming winter at best and starvation for many at the worst. What stands out in the Rune Poems talking about Hagalaz is that every one of them calls hail a grain. So the Rune obviously doesn’t just stand for destruction but also contains the seed for something new. Once a hailstorm has smashed the vegetation, the icy hailstones melt and water the ground so something new can grow…
When practicing magic this is a Rune that has to be handled with care. If you only practice magic in order to satisfy your basic needs for sex, money and power, best stay away from Hagalaz altogether. Where it can actually be useful is in the quest to transform the Self. When we embark on this journey of Self-transformation then we will meet Hagalaz if we want to or not as there are always structures that have to be removed before we can truly change and usually these have to be removed by force. Active use of Hagalaz makes sense in situations where the current behavior already creates a lot of damage, for example when suffering from some kind of addiction.