In Judgment, Evasive Aura is an early game Ritual. It is the first ritual you can learn and unlock that can be cast via the Holy Altar.
The time to cast to ritual duration ratio of evasive aura, as well as the relatively low cost of the ritual, ensures you can keep its effect consistently without much trouble.
The evasive aura basically halves the chance your task forces will encounter random events during their travels. For the most part, such random events tend to be less beneficial and this can be very important if your task force is already injured.