Attributes are a new mechanic added to Paragon in the The New Dawn patch. Each attribute affects your hero's stats, adds certain bonuses to your Hero and activates Gems if you buy a certain amount of an Attribute. You can also purchase Cards using Attributes.
There are 3 attributes in Paragon: Agility, Vitality and Intellect. Each attribute can be purchased up to 25 times for 1,000 gold each. Each purchase grants you a stat bonus, and whenever you reach a specific Tier (1, 7, 13, 19 and 25) a Gem assigned to that tier will activate.
Agility is best suited for combat. Each Agility point will give you 1.5 Attack Speed and 1.1 Basic Armor, except levels 1, 7, 13, 19 and 25, which give you:
Vitality is best suited for durability. Each Vitality point will give you 21.6 Max Health and 0.53 Health Regen, except levels 1, 7, 13, 19 and 25, which give you:
Intellect is best suited for casters. Each Intellect point will give you 12.6 Max Mana and 4.8% Mana Regen, except levels 1, 7, 13, 19 and 25, which give you: