Fighting sin can be a living hell. If a person is trying to renovate himself or become a better person without the gospel, the Word, the Spirit, and prayer, he is fighting Satan without any weapons. Thomas Watson called a person like this “the old Adam dressed in new clothes.” In reality, he is doomed at the outset of the battle; his life will either be a living hell of legalism, pride, or complete despair. John Owen put it this way.
“I…bewail the endless foolish labor of poor souls who, being convinced of sin and not able to stand against the power of thir convictions, do set themselves by innumerable perpelxing ways and duties to keep down sin: but being strangers to the Spirit of God, all in vain. They combat without victory, have war without peace, and are in slavery all their days. They spend their strength for that which is not bread, and their labor for that which profits not.”
He goes on.
“This is the saddest warfare that any poor creature can be engaged in. A soul under the power of conviction from the law, is pressed to fight against sin, but has no strength for the combat. They cannot but fight, and they can never conquer; they are like men thrust on the sword of the enemies, in purpose to be slain. The law drives them on, and sin beats them back. Sometimes they think indeed that they have foiled sin, when they have only raised a dust so that they see it not; that is, they distemper their natural affections of fear, sorrow, and anguish, which makes them believe that sin is conquered, when it is not touched.”
Rather than on our own, we need to put to sinful deeds to death by the Spirit (Rom 8.13), depending on Jesus’ work for us (Col 3.1-5), using the Word as our sword (Eph 6.17), and prayer as a great defense against sin (cf. Ps 51), always remembering that God’s grace sustains, motivates, and strengthens us for and in the battle (cf. 2 Cor 12.19). Owen explains gospel-driven mortification like this.
“Mortification of any sin must be by a supply of grace. Of ourselves we cannot do it.”
“Mortification of sin is peculiarly from the death of Christ.”
“In one word, this whole work [of mortification] which I have described as our duty, is affected, carried on, and accomplished by the power of the Spirit.”
This is a trustworthy saying: if you live according to the flesh you will die, but if by the Spirit you put to death the deeds of the body, you will live (Rom 8.13). Amen!