The first prayer, made with the hand and the voice together.
The name of the Trinity, spoken while tracing the Cross over the body.
When: At the beginning and end of every prayer, on waking, before meals, and when entering a church with holy water.
Why: It says in one gesture what we believe (one God in three Persons) and how we were saved (by the Cross). It is the sign we were marked with at Baptism.