Rav Yonason Eibschitz explains why we say ‘Hashem sefosai tiftach – G-d open my lips’ right before shemona esrei.  He explains that when man stands before the Master of the Universe, one’s vocal cords should freeze in paralysis, out of fear. We therefore offer a special prayer that G-d should grant us the fortitude to open our lips in prayer.  ~ Praying with Fire