Sword of Necessity

An ally, friend, or even foe lays bloodied and broken in front of you, and despite your oath you know you must take action against the evil that has been done. Speaking a word of forgiveness to your god, they grant you a mighty weapon of peace. 

This magic longsword lasts for 1 minute, and counts as a martial weapon with which you are proficient dealing 3d8 radiant damage on a hit. It deals an extra 1d8 against undead. The sword emits bright light in a 20 foot radius, and dim light for an additional 20.

At Higher Levels. When you cast this spell using a spell slot of 2nd level or higher, the damage increases by 1d8 for each slot level above 1st.