Abraham Booth, New City Catechism:

As the enemies of your soul are inveterate, subtle, and powerful, and your spiritual frames inconstant, it is highly necessary you should live under a continual remembrance of those awakening considerations. What more advisable, what so necessary for you, as to walk circumspectly; to watch and pray, lest you enter into temptation? A sense of your own weakness and insufficiency, should ever abide on your mind and appear in your conduct. As the corruption of nature is an enemy that is always near you, and always in you, while on earth; and as it is very strongly disposed to second every temptation from without; you should “keep your heart with all diligence.” Watch, diligently watch, over all its imaginations, motions, and tendencies. Consider whence they arise and to what they incline, before you execute any of the purposes formed in it. For such is the superlative deceitfulness of the human heart, “that he who trusteth in it is a fool,” ignorant of his danger, and unmindful of his best interests. This consideration should cause every child of God to bend the suppliant knee, with the utmost frequency, humility, and fervour: to live, as it were, at the throne of grace; nor depart thence till far from the reach of danger. Certain it is, that the more we see of the strength of our adversaries and of the danger we are in from them, the more shall we exercise ourselves in fervent prayer. Can you, O Christian, be cool and indifferent, be dull and careless, when the world, the flesh, and the devil are your implacable and unwearied opposers?