If you feel sweetness or compunction at some word of your prayer, dwell on it; for then our guardian angel is praying with us. St. John Climacus, "The Ladder of Divine Ascent," (Boston: Holy Transfiguration Monastery, 1978), Step28: On Holy and Blessed Prayer, the Mother of Virtues, and on the Attitude of Mind and Body in Prayer) In the presence of an invisible spirit, the body becomes afraid; but in the presence of an angel, the soul of the humble is filled with joy. Therefore, when we recognize the presence from the effect, let us quickly hasten to prayer, for our good guardian has come to pray with us. St. John Climacus, "The Ladder of Divine Ascent," (Boston: Holy Transfiguration Monastery, 1978), STEP 21: On Unmanly and Puerile Cowardice The angel who is always near us is by nothing so distressed and made indignant as when, without being constrained by some necessity, we deprive ourselves of the ministration of the Holy Mysteries and of reception of Holy Communion, which grants remission of sins. For at that hour the priest offers up the sacrifice of the Body of Him Who gives us life, and the Holy Spirit descends and consecrates the Body and Blood and grants remission to creation. The Cherubim, the Seraphim, and the angels stand with great awe, fear, and joy. They rejoice over the Holy Mysteries while experiencing inexpressible astonishment. The angel who is always by us is consoled, because he also partakes in that dread spectacle and is not deprived of that perfect intercourse. St. Isaac the Syrian When you close the doors to your dwelling and are alone you should know that there is present with you the angel whom God has appointed for each man...This angel, who is sleepless and cannot be deceived, is always present with you; he sees all things and is not hindered by darkness. You should know, too, that with him is God, who is in every place; for there is no place and nothing material in which God is not, since He is greater than all things and holds all men in His hand. St. Antony the Great (On the Character of Men no. 62) See http://www.orthodox.net/gleanings/guardian_angel.html