From Parochial and Plain Sermons

by Venerable John Henry Newman:

And since prayer is not only the weapon, ever necessary and sure, in our conflict with the powers of evil, but a deliverance from evil is ever implied as the object of prayer, it follows that all texts whatever which speak of our addressing and prevailing on Almighty God, with prayer and fasting, do, in fact, declare this conflict and promise this victory over the evil one. Thus in the parable, the importunate widow, who represents the Church in prayer, is not only earnest with God, but against her adversary. "Avenge me of mine adversary," she says; and our "adversary" is "the devil, who, like a roaring lion, walketh about seeking whom he may devour; whom resist," adds St. Peter, "stedfast in the faith." Let it be observed that, in this parable, perseverance in prayer is especially recommended to us.