Mageblade classes all focus in something specific. For example fighters have a bonus in combat rolls. This bonus is called Focus, and it depends only on the character level, starting at +3 at level 1, so level 1 fighters have +3 to hit.
Rogues focus on luck, which means they have Focus free rerolls every day. They can use those for initiative rolls, skill rolls, damage rolls, even to hit rolls that hit them.
This is interesting because it essentially gives rogues the ability to get away with something if they really really need to. I really really need to climb that wall? To win initiative and leg it? To vanish in the crowd? Reroll until you succeed.
To hit someone’s face? It gets better. Not only you can reroll to hit, but this has an additional effect: critical hits proliferation. Each character has a 5% chance of a critical in combat. But if you miss and reroll you have another 5% chance. And at level 1 you can reroll 3 times a day, which makes for a bit less than 19% of taking a critical hit, if they decide to dump their luck in a single round, for example if cornered.
That would not be the most effective use of rerolls though: simply rerolling on a miss is more effective, and stretches the Focus a bit more.