The Institutes, Book 3
No Going Back to Bed After the Morning Office
But some in this province, not knowing why this office was appointed and introduced, go back to bed after their morning prayers are finished, and in spite of it fall into the very habit our elders instituted this service to check. For they are eager to finish it at that hour, so that those inclined to be indifferent and not careful enough may have a chance to go back to bed again. That most certainly ought not to be done, as we showed more fully in the previous book when describing the service of the Egyptians. For the force of our natural passions may be roused and stain the purity we gained by humble confession and prayers before the dawn; or some illusion of the enemy may defile us; or even the rest of a pure and natural sleep may break the fervor of our spirit and make us lazy and slothful the whole day long, chilled as we are by the sluggishness that sleep brings.
To avoid this the Egyptians, especially as they are used to rising at fixed times even before cockcrow, prolong their vigils afterward, once the canonical office has been celebrated, right up to daylight. So the morning light, when it comes on them, finds them settled in fervor of spirit, and keeps them still more careful and fervent all through the day, since it has found them prepared for the contest and strengthened against their daily struggle with the devil by the practice of night vigils and spiritual meditation.