Shield barrier scales purely from your attack power, then a multiplier is added on top of everything from resolve. More strength = better barrier. More mastery = better barrier (It increases attack power). More crit / haste = more rage = more barriers / higher rage barriers. Vers/MS = no impact with barrier, but has their own mechanics to reduce damage or recover from it.
I'm not saying its a good ability, but I still use it. Health bars don't spike anymore from damage or heals, including absorbs. Just have to deal with it.