Prayer is not only useful to us, but necessary for salvation. Hence it is that God, because He desires that we should all be saved, has enjoined it on us by a precept. “Ask, and it shall be given you.” (Matthew 7:7). Jesus Christ says, that men “ought always to pray.” (Luke 18:1). He does not say it is useful or benefitting, but that men “ought always to pray.” Wherefore, the Doctors of the Church justly say that a man cannot be excused from grievous [i.e., mortal] sin who neglects to recommend himself to God at least once in a month and whenever he finds himself assaulted by any strong temptation.