Prof. Louis Berkhof (1873-1957): “Sanctification: It is a work of God in which believers co-operate. When it is said that a man takes part in the work of sanctification, this does not mean that man is an independent agent in the work, so as to make it partly the work of God and partly the work of man; but merely, that God affects the work in part through the instrumentality of man as a rational being, by requiring of him prayerful and intelligent co-operation with the Spirit. That man must co-operate with the Spirit of God follows: (a) from the repeated warnings against evils and temptations, which clearly imply that man must be active in avoiding the pitfalls of life, Rom. 12:9, 16-17; 1 Cor. 6:9-10; Gal. 5:16-23; and (b) from the constant exhortations to holy living. These imply that the believer must be diligent in the employment of the means at his command for the moral and spiritual improvement of his life, Micah 6:8; John 15:2, 8, 16; Rom. 8:12-13; Rom. 12:1-2, 17; Gal. 6:7-8, 15.” (Berkhof, Systematic Theology, 534)