Nefesh HaChayim, Reb Itzele's Long Annotation

And the vessels of the heart/mind and the five products of the mouth475The five classes of sounds that the mouth produces: guttural, labial, palatal, lingual and sibilants are vessels to infuse its energy into the three mother letters alef, mem and shin, according to how they combine so that they will be directed to none other than God, and his speech will be about them and not about worthless things.