Sanctification is the work of the Holy Spirit in us whereby our inner being is progressively changed, freeing us more and more from sinful traits and developing within us over time the virtues of Christlike character.
We are 100 percent responsible for the pursuit of holiness, but at the same time we are 100 percent dependent upon the Holy Spirit to enable us in that pursuit. The pursuit of holiness is not a pull-yourself-up-by-your-own-bootstraps approach to the Christian life.