Blessing of Light
The Blessing of Light is a power bestowed upon Warriors of Light chosen by Hydaelyn distinct from the Echo. The Blessing of Light is tied to and further empowered by the Crystals of Light obtained by Hydaelyn's champions, who manifest these crystals by their deeds.
The Blessing of Light provides protection from aetherial corruption, such as tempering by |primals, wards the allies of Hydaelyn's champions against intrusion by Her enemies (though the three Ascians of the Source are capable of bypassing this), and allows Her to intervene directly on their behalf to perform miraculous feats. During the battle with The Ultima Weapon, Hydaelyn uses the Blessing of Light to strip the Armor of Darkness and the essences of the primals Ifrit, Titan, and Garuda from the machine. She then uses it to ward her champions against the spell Ultima, though by doing so She injures Herself and permanently impairs Her ability to intervene and communicate.
During the Warrior of Light's adventure in the First, the Blessing of Light was used to absorb the power of the Lightwardens. However, even with a fully-empowered Blessing of Light, the Warrior of Light was unable to fully withstand the primordial Light absorbed from these creatures and almost succumbed to a sin eater transformation. It is later used to break free of the chains cast upon the Warrior of Light and summoned champions from beyond the Rift by Hades and protect them from his power of Darkness.
In Final Fantasy XIV: Endwalker, the Warrior of Light learns that the Blessing of Light is actually a spell called the Traveler's Ward cast by the Ancient Venat, the true identity of Hydaelyn and former holder of the seat of Azem. The ward specifically protects against aetheric corruption, and the magic is unique enough for the Venat of the past to recognize it as her own spell despite bestowing it on the Warrior of Light millennia in the future.