You create a protective ward that has 18 hit points. When you take a single source of damage, this ward will protect you by absorbing up to its total number of hit points. Once the ward has absorbed damage, you are able to release the energy absorbed by the ward as force damage on the next source of damage that you do to a single target.

At Higher Levels: When you cast this spell using a spell slot of 4th level or higher, the ward gains 6 hit points for every slot level above 3rd.