St. Dimitry of Rostov 1651-1709
Man is dual in nature: he is external and internal, fleshly and spiritual… And there are two kinds of learning – the external and the internal: the external through books, the internal through meditation on God; the external through the love of wisdom, the internal through the love of God; the external in rhetoric, the internal in prayer; the external through wittiness, the internal through warmth of the spirit… Prayer is also two-fold – external and internal: that which is said in front of others and that which is said secretly; that which is conducted in concert with others and that which is read alone; that which must be read and that which is voluntary… The former is read out loud with the voice, the latter only by the mind. The former is read standing, the latter not only while standing or walking, but also lying in bed, in other words, at all times whenever one raises his mind to God… Interior prayer… requires neither a mouth, nor books, nor movements of the tongue, nor the voice in one’s throat… but only the lifting of the mind to God and meditation, which can be done in any place. (Met. Hilarion Alfeyev, Vol. I Orthodox Christianity: The History and Canonical Structure of the Orthodox Church. The Russian Church in the Synodal Period, pg. 191)