The spell captures some of the incoming energy, lessening its effect on you and storing it for your next melee attack. You have resistance to the triggering damage type until the start of your next turn. You can choose to mirror it or keeping it to cast at another time.

At Higher Levels. When you cast this spell using a spell slot of 3rd level or higher, the extra damage increases by 2d6 for each slot level above 1st.