Shri Mahamrityunjaya Mantra

Om Tryambakam Yajamahe

Sugandhim Pushtivardhanam

Urvarukamiva Bandhanan

Mrityor Mukshiya Maamritat

We Meditate on the Three-eyed reality
Which permeates and nourishes all like a fragrance.
May we be liberated from death for the sake of immortality,
Even as the cucumber is severed from bondage to the creeper.

Mahamrityunjaya Mantra (maha-mrityun-jaya) is one of the more potent of the ancient Sanskrit mantras. Maha mrityunjaya is a call for enlightenment and is a practice of purifying the karmas of the soul at a deep level. It is also said to be quite beneficial for mental, emotional, and physical health.
AUM/OM: Absolute reality.
Tryambakam: Trya means three. Ambakam means eyes. It means the three eyes of the Absolute, which are the processes of creation, existence, and dissolution, as well as the other triads, which are part of AUM. The three "eyes" means experiencing these three stages and triads at one time, from the higher, all pervasive vantage point of the Absolute.
Yajamahe: We rejoice in meditation on all of this.
Sugandhim: Means fragrance. Like a spreading fragrance, all of this permeates the whole of existence, while at the same time being that existence
Pushtivardhanam: Means that which sustains and nourishes all. Thus, the fragrance that permeates all is the sustainer of all beings, while also the essence of all beings.
Urvarukamiva: Urva means big and powerful. Arukam means disease, like the spiritual diseases of ignorance and untruth, which are like the death of Wisdom or Truth.
Bandhanan: Means bound down, as in bound down to the ignorance and untruth.
Mrityor: Means ignorance and untruth.
Mukshiya: Means liberation from the cycles of physical, mental, and spiritual death.
Maamritat: Means please give me rejuvenating nectar, so as to have this liberation, like the process of severing the cucumber from the creeping vine.
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40 day practice
The period of 40 days has been widely recognized as an auspicious period both in the East and the West since ancient times. A traditional way to do an extended mantra practice is to choose a number of repetitions per day, and to do that for 40 days. The mind likes to have a beginning and end to a practice, a sense of completion, such as comes with a 40 day (or longer) practice.