He who does not have attention in himself and does not regard his mind, cannot become pure in heart, and so cannot see God. He who does not have attention in himself cannot be poor in spirit, cannot be contrite, nor be gentle and meek, nor hunger and thirst after righteousness, nor be merciful, nor a peacemaker, nor suffer persecution for righteousness sake.

Saint Symeon the New Theologian (949 – 1022)