The great spiritual classic The Imitation of Christ presents these sentiments to reflect upon before Holy Communion:
O my God, how hard these men tried to please You! Alas, how little is all that I do! How short the time I spend in preparing for Communion! I am seldom wholly recollected, and very seldom, indeed, entirely free from distraction. Yet surely in the presence of Your life-giving Godhead no unbecoming thought should arise and no creature possess my heart, for I am about to receive as my guest, not an angel, but the very Lord of angels. - Book Four, chapter 1