Vigilance and prayer should be as closely linked together as the body to the soul, for the one cannot stand without the other. Vigilance first goes on ahead like a scout and engages sin in combat.
Symeon the New Theologian argues that vigil-as-vigilance and prayer are organically inseparable—vigilance precedes prayer as a scout precedes battle, making their union the gate between spiritual life and death.
, The Philokalia, Volume 4, 1995thesis