The earliest D&D games had three classes; the mage, the fighter, and the thief. The Mage has evolved into several different kinds of spellcasters, and in Baldur's Gate 3, players can build Warlocks, Sorcerers, Bards, and Wizards to satisfy their magical urges. Other classes can also learn magical spells through items, multiclassing, and subclasses.
The school of Abjuration consists of defensive spells. It doesn't get the same attention as Evocation, which blows things up; or Illusion, which can make things appear or disappear. However, it might be the most essential and useful of all the magical schools, because it keeps the squishy casters from getting crushed. This is the school of shielding spells, better dice rolls, and improved AC. After all, a character can't cast spells at all if they're dead.
8 Armor of Agathys
This spell is available to Warlocks as a cantrip, which means they can use it as often as they want, but it can only be used on the caster themself. It has a long duration, lasting until the Warlock's next long rest, unless otherwise removed by certain spells or the character dies.
It covers the caster in a spectral frost that not only gives them five temporary hit points, but does does five cold damage to anyone that touches them in melee range. As such, Armor of Agathys is especially useful to Warlocks who like to fight in melee range.
7 Blade Ward
This standard protection spell is available to a variety of classes, as either a learned spell or a cantrip. Blade Ward gives the target resistance to slashing, bludgeoning, or piercing damage. That means a character has a better chance against both melee and ranged attacks.
The spell only works on the caster and lasts for a mere two turns, which is why it's nice to have it as a cantrip as opposed to taking up a spell slot. It's intended to be used as a combat spell, so make it count.
6 Resistance
Resistance improves the target's chance against saving throws. Like many other spells in the Abjuration school, this spell can be equally useful outside of combat, like to help a character beat a saving throw against a poison or damage over time (DoT) effect. It lasts for ten turns. It's comparable to Guidance, a Divination spell that has a passive effect on certain dice rolls.
It can be cast on others and the caster themselves, and gives them a 1d4 improvement to every saving throw. That means checks to Concentration, Survival, Perception, and even Stealth and Lockpicking.
5 Shield
Another spell that can only be used on the caster, Shield is equally nice for armor-wearing classes that want to avoid a certain type of magical damage. Shield increases the target's armor class by 5 when an enemy is within striking range, which is how it mitigates melee damage. Unlike other spells of this nature, it can be cast on a character already wearing armor.
Another nice perk is protecting the caster from Magic Missile, one of the more effective and lethal combat spells from the Evocation school. It lasts until the caster takes a long rest or dies.
4 Protection From Evil And Good
This isn't the old spell from the D&D universe that protects the caster or their allies from characters, creatures, or NPCs of a certain moral alignment. It protects against any creature that's either good or evil, an eclectic group that includes celestials, demons, elementals, and aberrations, to name a few.
These creatures can still attack the target, but most do so at a disadvantage, and they can't Charm or Possess them, either. The spell lasts until the target takes a long rest.
3 Mage Armor
This spell is for any caster, but best for those that have a high Dexterity score, so Bards, Warlocks, and Druids for certain. It gives them an armor class of 13, then adds their Dexterity stat, giving the usual squishy caster a more than decent AC.
This spell only works on a target that isn't already wearing armor, and lasts until the target takes a long rest. Wizards and Sorcerers often know this spell as a cantrip or from their level one spell tier list, since they often can't wear armor at all.
2 Aid
This handy spell also appears on a variety of trinkets, which is great because Fighters and Rogues can make use of it just as easily. Any ability that grants the character extra hit points or a healing spell is always helpful.
Aid gives the caster or their target some healing along with increasing their maximum hit points. Normally, it's a spell that Bards, Rangers, and other support classes have as a cantrip, while other classes can learn it at higher levels.
1 Pass Without Trace
If Rogues had casting powers, they would love this spell, but it's currently only available to Druids, Rangers, and Druids of the Trickery Domain. Pass Without Trace veils the party in silence and shadows, giving them a +10 bonus to Stealth checks.
The caster uses it on themselves, but it affects every ally within a nine-meter radius. It lasts until the next long rest and is subject to Concentration checks.