Lore of Light is one of the strongest lores in the game. Net of Amyntok is the single most reliable means of completely stopping an enemy in their tracks. Other characters abilities and spells can slow an enemy, but won't fully stop them. Net an enemy lord and snipe them with missiles or charge them with your lord, stop heavy cav before it shocks your archers, giving time to reposition or counter charge.
Pha's Protection is another good spell for protecting units from heavy damage. Melee defense is one of the most important stats in the game and +35 melee defense is an absurd amount, doubling most unit's melee defense. Birona's Timewarp is a strong spell for aggressive bursts of intense fighting. Save it for key engagements.
Shem's gaze is a decent missile spell, best used for whittling down large targets or sniping characters, as well as triggering the lore passive. Finally, Banishment is a strong vortex spell that will destroy blobs of infantry. Beware its random nature.
Light of Battle simply imbues unbreakable in an area for 22 seconds. Overcast boosts the duration to 44 seconds. It is quite niche.