Do Not Raise Your Voice in Prayer

Do Not Raise Your Voice in Prayer to HaShem (Shmoneh Esreh)

ברכות לא - אורח חיים ק"א סימן ג '

טוררמב"םבית יוסףזוהר (פנימיות התורה)“Side” issur to pray loudly as if G-d cannot hear (lack of faith)
Prayer like speaking
מבקש צרכיוSpeak quietly due to awe in the presence of the King
Proper intention
עבודה שבלבRequires quiet speech
Loud prayer would disturb oneself
In the World of Atzilus, world of unity, to stand before G-d in complete bitulWords not even heard by one’s own ears

Based on Lekutei Sichos חלק לה' פרשת ויגש

The Holy Zohar says this verse alludes to the concept that in prayer sometimes the sound is heard and sometimes the sound is not heard (the “silent” Amidah as learned from Chanah)