Damage, rather than forcing a Concentration roll and using up valuable dice during combat, adds +1 to the DR of any pending Wielding effects for each point of damage suffered. Ongoing ‘sustained’ effects (Agony, for example) will be ‘lost’ if the total DR goes over the amount rolled.
Example: Greg is wielding an Energy-Salvation effect with a DR of 23, and has no Concentration or Alertness ranks. He gets shot for 6 damage, which raises his DR for the effect to 29.
Ranks in concentration and Alertness allow you to ignore up to their total value in damage before the damage begins to affect your Wielding DR.
Example: Alan, like Greg, is Wielding to create an Energy-Salvation effect with DR 23; unlike Greg, he has 2 ranks of Alertness and 5 ranks of Concentration. He gets shot for 6 damage, but the combined 7 ranks of Alertness and Concentration permit him to ignore the damage, keeping his DR at 23. The next segment, he gets shot for a further 4 damage; he ignores one point of the damage, while the other three (and all future shots while attempting the check) raise the DR to 26.