Source: Player's Handbook
Prerequisite: Level 4+, Spellcasting or Pact Magic Feature
You gain the following benefits.
Ability Score Increase. Increase your Intelligence, Wisdom, or Charisma score by 1, to a maximum of 20.
Concentration. You have Advantage on Constitution saving throws that you make to maintain Concentration.
Reactive Spell. When a creature provokes an Opportunity Attack from you by leaving your reach, you can take a Reaction to cast a spell at the creature rather than making an Opportunity Attack. The spell must have a casting time of one action and must target only that creature.
Somatic Components. You can perform the Somatic components of spells even when you have weapons or a Shield in one or both hands.