You concentrate on wisdom passed down from your predecessors to gain greater capacity to work your magic.  Select three spells at random from among spells in your spellbook you do not have prepared.  For the duration of this spell, you can cast those spells as though you had them prepared.  If you cast a spell requiring concentration this way, you continue to be able to cast it for that spell's duration.  You cannot cast this spell again until after you have completed a long rest.