It is the object of Satan to keep those secure who are safe in his hands; nor does God see fit to disturb their quiet. But on the other hand, where Satan perceives a work of grace going on, where he sees the eyes sometimes filled with tears, where he hears the sobs heaving from the contrite heart, where he observes the knees often bent in secret prayer, where his listening ear often hears the poor penitent confess his sins, weaknesses, and backslidings before God, (for by these observations we have reason to believe Satan gains his intelligence,) wherever he sees this secret work going on in the soul, mad with wrath and filled with malice, he vents his hellish spleen against the objects of God's love. Sometimes he tries to ensnare them into sin, sometimes to harass them with temptation, sometimes to stir up their wicked heart into desperate rebellion, sometimes to work upon their natural infidelity, and sometimes to plague them with many groundless doubts and fears as to their reality and sincerity before a heart-searching God.
So that whilst those who have no work of grace upon their hearts at all are left secure, and free from doubt and fear, those in whom God is at work are exercised and troubled in their minds, and often cannot really believe that they are the people in whom God takes delight. The depths of human hypocrisy, the awful lengths to which profession may go, the deceit of the carnal heart, the snares spread for the unwary feet, the fearful danger of being deceived at the last—these traps and pitfalls are not objects of anxiety to those dead in sin. As long as they can pacify natural conscience, and do something to soothe any transient conviction, they are glad to be deceived.
But, on the other hand, he that has a conscience tender in God's fear knows what an awful thing it is to be a hypocrite before God, to have "a lie in his right hand," and be deluded by the prince of darkness; and therefore, until God himself with his own blessed lips speaks with power to his conscience, and establishes him in a blessed assurance of his interest in Christ by "shedding abroad his love in his heart," he must be tried and exercised in his mind, he must have these various tossings to and fro, for this simple reason—because he cannot rest satisfied except in the personal manifestations of the mercy of God.