What is Blessed Shots?

[Hank Hill's Disappointed Sigh]

what does it do?

[Pungent]

When the passive ability is up (every 10 seconds or every time you get a melee kill), your next ranged weapon shot will be a guaranteed critical hit. Crits do much more damage, bypass armor, and can trigger other effects if you equip certain traits on your weapon (e.g. gain 2 ammo on crit hit, +25% power against enemies of the same armor type, reduce cooldown timer of your active ability).

It's right there in the description.