Fortunately, religious Hebrew people kept on saying and singing the “Shema” (trans. “Hear”)even though it was not scientifically proven.
The polyvagal theorist Stephen Porges Ph.D. has informed us that there is a physiologic basis for calming us down which we can recognize is demonstrated in the ancient practice of Shema. (As far as I know, Porges has not mentioned this connection with the Shema and his theories, though he is doing research on music and his polyvagal theories.)
Early studies by Porges included one with the Rolfer John Cottingham, which you can read about here. http://stephenporges.com/index.php/scientific-articles/publicationss/16-shifts-in-pelvic-inclination-angle-and-parasympathetic-tone-produced-by-rolfing-soft-tissue-manipulation
Now, back to the Shema. When we take an in-breath, the heart rate speeds up, and when we release an out-breath the heart rate slows down. We know this physiological fact now. In the olden times and today religious practitioners go for a peaceful feeling, union with a religious sense, a declaration of faith.
To try the ancient practice in a meditative manner, take a quick medium-to-big gasp of in breath and say on the out breath “Shemaaaaaaaaaaa” for about 3 or 4 seconds. Actually count, 1 thousand, 2 thousand, 3 thousand to yourself while saying “Shemaaaaaaa”. There are more words to this prayer, but just say the word, “Shemaaaa” 6 times in that manner.
Remember, there weren’t clocks in those days, and on the Sabbath there was all day to pray. If you don’t immediately feel more peaceful, see how many repetitions of short in breath and long out breath it will take to slow your stressful heart including the beat and the blood pressure down. This prayer is often said by religious as a meditation 2 or 3 times a day.
Or— instead of the above wordiness— sing along with this one a few times. https://www.youtube.com/watch?v=_LEPn2KZnuY
And now—-OOOOOOOOOOOOOOOOMMMMMMMMMMM (gasp) OOOOOOOOOOOOMMMMMMMM(just to show that other cultures could get with the polyvagal theory)