The last thing the Dragonborn would ever want was to harm someone willingly, unless attacked first. Erandur would tell the warrior was uneasy with his magics. "Rest easy, friend. I am using magic, but only to heal." He spoke with a smile on his face, trying to be reassuring as Artorias sat down.
Carefully taking steps forward his hands lit up in a white light when he reached the warrior. His hands then went to the source of the darkness, the light shining brighter when they made near contact. The glow of the spell engulfing his arm. Soon, the darkness would begin receding away from his shoulder and neck, strands of the darkness being poured out into the soul gems, capturing it.
But, it tried to fight back, something of a tendril slashed Erandur across the cheek. Only a grunt would be its answer, Erandur gritted his teeth as the light shined brighter, pulling more and more of the darkness out.