Prayer is War

...the spiritual poison...is injected by the enemy powers into the mind of any who neglect prayer and who do not observe the words of Paul, following the exhortations given by Jesus, that we should "pray ceaselessly." For like a dart from the soul of the one who prays with knowledge and with reason or by faith will it go forth from the saint, and wound to destruction and dissolution the spirits which are hostile to God, those who desire to truss us with the bonds of sin.

Origen, On Prayer, 12