Isaiah

“Now, it being our duty to mortify, to be killing of sin whilst it is in us, we must be at work. He that is appointed to kill an enemy, if he leave striking before the other ceases living, doth but half his work, Gal. vi. 9; Heb. xii. 1; 2 Cor. vii. 1.”
― John Owen, Of the Mortification of Sin in Believers

“The contest is for our lives and souls. Not to be daily employing the Spirit and new nature for the mortifying of sin, is to neglect that excellent succour which God hath given us against our greatest enemy. If we neglect to make use of what we have received, God may justly hold his hand from giving us more. His graces, as well as his gifts, are bestowed on us to use, exercise, and trade with. Not to be daily mortifying sin, is to sin against the goodness, kindness, wisdom, grace, and love of God, who hath furnished us with a principle of doing it.”
― John Owen, The Mortification of Sin

“When, therefore, men have slight and transient thoughts of their lusts, it is no great sign that they are mortified, or that they are in a way for their mortification. This is every man’s “knowing the plague of his own heart,” 1 Kings viii. 38, without which no other work can be done. It is to be feared that very many have little knowledge of the main enemy that they carry about with them in their bosoms”
― John Owen, Of the Mortification of Sin in Believers

“Still, in studying their writings, we have endeavoured to remember (1 Cor. 3:21-23; see also Augustin. Ep. 28), that all things are ours, to serve, not lord it over us, but that we axe Christ’s only, and must obey him in all things without exception. He who does not draw this distinction will not have any fixed principles in religion; for those holy men were ignorant of many things, are often opposed to each other, and are sometimes at variance with themselves.”
― John Calvin, Institutes of the Christian religion Volume v.1