VWhen the synagogue falls quiet and we say the silent Amidah prayer, we are not to let others hear our voices. The Talmud learns this from the bible story of Hannah. When she prayed for a child, “only her lips moved, but her voice could not be heard” (I Samuel, 1:13). The Talmud infers from this verse from this, “one’s lips should form the words . . . but one should not raise his voice” .
Articulating prayer is important and helps us focus on what we want to say, but we should not pray loudly. Why should we be careful to not allow those around us to hear our prayers?
Obviously, we don’t want to disturb or distract other people, but there are other reasons too. The Mishnah Berurah adds that those who raise their voices in prayer are of little faith, as if they don’t believe that God hears a silently whispered prayer(Orach Chaim 101:6).