Oftentimes men charge that upon the devil that is to be charged upon their own hearts
Though Satan has his devices to draw souls to sin, yet we must be careful that we do not lay all our temptations upon Satan, that we do not wrong the devil, and attribute that upon him that is to be attributed upon our own base hearts.
Sin and shifting blame came into the world together. This is no small baseness of our hearts, that they will be wicked, ay, very wicked, and yet will attribute that wickedness upon Satan.
Man has an evil root within him
Were there no devil to tempt him, nor no wicked men in the world to entice him, yet that root of bitterness, that cursed sinful nature that is in him, would draw him to sin, though he knows beforehand that “the wages of sin is eternal death” (Rom 6:23), “for out of the heart proceed evil thoughts, murders, adulteries, fornication, thefts, false witnesses, blasphemies” (Matt 15:19).
The whole frame of man is out of frame
The understanding is dark, the will cross, the memory slippery, the affections crooked, the conscience corrupted, the tongue poisoned, and the heart wholly evil, only evil, and continually evil. Should God chain up Satan, and give him no liberty to tempt or entice the sons of men to vanity or folly, yet they would not, yet they could not but sin against him, by reason of that cursed nature that is in them, that will still be a-provoking them to those sins that will provoke and stir up the anger of God against them (Jude 15, 16).
Satan hath only a persuading sleight, not an enforcing might
He may tempt us, but without ourselves he cannot conquer us. He may entice us, but without ourselves he cannot hurt us. Our hearts carry the greatest stroke in every sin. Satan can never undo a man without himself; but a man may easily undo himself without Satan. Satan can only present the golden cup, but he hath no power to force us to drink the poison that is in the cup. He can only present to us the glory of the world, he cannot force us to fall down and worship him. He can only spread his snares, he hath no power to force us to walk in the midst of his snares.
Therefore do the devil so much right, as not to excuse yourselves, by your accusing him, and laying the load upon him, that you should lay upon your own hearts.
Adapted from The Complete Works of Thomas Brooks, 1:152–153.