Precision is a talent in the Protection tree, you will need to spend 8 points in Protection to max it.
This is an important talent for most Retribution Paladins as it is a solid increase in their damage output.
Most tankadins also max it, as it increases threat generation as well as reduces the missing chance of Righteous Defense.
With 3 points in this skill you still need to attain 95 hit rating at level 70 to be able to hit raid bosses without misses. (As of Patch 2.3)
As per Patch 2.3 patch notes: The chance for Righteous Defense to land successfully on its targets is now increased by hit rating. Previously, RD used spell hit rating which is scarce on traditional tanking gear.