You need a powersource:
https://everquest.allakhazam.com/search.html?q=energeian Each powersource adds different stats, the lower ones are crafted with tradeskills, and the good ones are bought in Katta Castrum once you have sufficient faction, and an alternate currency called Orum.
The purity stat on infusible armor and weapons is a percentage of how much of the powersource's stats you will get when you equip it. Both armor and weapons will get stats, and weapons will also get a proc.
The more infusible stuff you have the faster the powersource will drain. When it burns out, you have to get a new one.
This is a page detailing the stats that each powersource adds based on certain purity values:
http://www.eqwiki.net/wiki/Combine_Power_Sources
Hope that helps!