In addition to the normal effect, your Judgement of the Crusader spell will also increase the critical strike chance of all attacks made against that target by an additional X%.
Improved Seal of the Crusader is a talent in the Retribution tree, you will need to spend 8 points in Retribution to max it.
This talent is the main utility of Retribution Paladins. Not only does the normal Judgement increase the Paladin's damage, but the increased critical strike chance greatly increases the entire raid's damage output as well. Considered a "must have" talent for all Retribution Paladins.