The word mantra has two parts: "man," which in Sanskrit means "mind," and "tra," which means "instrument." A mantra is therefore an instrument of the mind, a powerful sound or vibration that you can use to enter a deep state of meditation.
Silently repeating a mantra as you meditate is a powerful way to enter the silence of the mind. As you repeat the mantra, it creates a mental vibration that allows the mind to experience deeper levels of awareness. The mantra then becomes increasingly abstract and indistinct, until you're finally led into the field of pure consciousness from which the vibration arose—your spirit.
Since each mantra induces specific vibrations in the mind, Deepak uses a variety of them throughout the Experience to align with his daily message and meditation. You may already be aware of some mantras. For instance, one mantra you may have heard is So Hum (I am). Another mantra you may know is Sat, Chit, Ananda (Existence, Consciousness, Bliss). You'll use both mantras at various times throughout the Experience.
When mantras are silently repeated during meditation, they help us disconnect from the thoughts filling our mind and slip into the gap between thoughts. Think of mantras as ancient power words with subtle intentions that help us connect to spirit, the source of everything in the universe.