Why are Mantras used in many religions

There are many prayers that could be considered Mantras even in Christianity. For example, my mother's childhood prayer in the 1920s was:

Now I lay me down to sleep

I pray the Lord my soul to keep

If I should die before I wake

I pray the Lord my Soul to take.

This prayer was given by many many children especially in the 1920s. However, since children died a lot then this is why "I pray the Lord my Soul To take" is there. Whether this comforted children or just scared the hell out of them both are likely true.

However, fear was used much more to control children before about 1970 too here in the U.S. it's just the way it was when I grew up in the 1950s.

for example, in Buddhism there is the Tara Mantra that I personally see as a mother diety similar to Mother Mary the Mother of Jesus:

The primary Sanskrit mantras for Goddess Tara include the Green Tara mantra, the White Tara mantra, and the fierce Tantric Tara mantra 

Green Tara Mantra (Universal/Liberation)

Sanskrit: Om Tare Tuttare Ture Svaha
Meaning: I bow to the liberator, mother of all buddhas. [1, 2]

When I was in Dharamshala I got a Poster of all of the 21 Taras for example that I brought home to the U.S. in 1986 after being in India and Nepal from December of 1985 until April of 1986 with my family. I was 37 at the time.

Then also I consider the Hail Mary prayer to also be a mantra:

Which goes something like:

Hail Mary full of Grace

The Lord is with thee

Blessed Art thou among Women

And blessed is the fruit of your womb Jesus

Though there are also much longer versions of this I see this grouping of words as a mantra too in that you repeat this mantra over and over again.

What this does is it creates visualizations in your mind of Mary saving you and your family just like the Tara Mantra gives you visualizations of Tara Saving you and your family.

It's a way to get beyond your fears and terrors of the world by placing a mantra and visualizations of positive things in your life and your family's life too.

Especially during difficult times prayer mantras can help a person focus on what they want in their lives rather than having their emotions and minds explode in Chaos and confusion.

So, it is a way to focus yourself through prayer so you don't explode completely with emotions that can be destructive if they are not utilized properly through prayer.

Others might define all these things differently than I do but this is my personal experience with Christian and Tibetan Buddhist Mantras.

By God's Grace