The question is simple! Why are you playing a priest?
For me, I rerolled from rogue in the first few weeks of vanilla to priest. As a true n00b, I've levelled as holy and by god this took long. Not to mention dying so much. However hitting level 60 was a major achievement!
My first completed set was tier 0 and my first ever epic was Darkmoon Card : Blue Dragon. Kept DMC till deep into Naxxramas, the regen bonus of this trinket was amazing.
These days I'm holy with shadow as offspec. Holy is my prime spec, always have been but it is really nice to swap to Shadow to do some solo play.