You will be able to pick 2 of 4 available runes when you are done choosing skills. Theese runes will provide passive bonusses and may boost your skillset, so check carefully when picking so you can create functional skillsets.
COMBAT RUNE:
"If they move, kill them. In fact, kill one now to make sure the other understands"
Combat provides 40 permanent bonus damage. Enemies killed will also provide double rage.
HONOR RUNE:
"Your sword will rust and your arrows will crack, but your honor can't die, it will remain there... forever."
Honor provides 10 points to all atributes. It also reduces the rage limit from 80 to 70.
SPIRIT RUNE:
"Slow and steady may not always win the race, but at least it doesn't end up splattered on the walls"
Spirit provides 600 bonus starting life. Healing Orbs dropped by enemy monsters will heal 50% more hp as usual and will also regenrate mana.
FANATISM RUNE:
"Change your mind or i'll change it for you."
Fanatism provides 60% lifesteal and 25% increased attack speed.
Each rune will upgrade 16 of the 21 total skills (including ultimates), meaning that there are 5 abilities that won't get affected by each particular rune. Yet again, pick wisely!