How Do I Mature Spiritually and Grow in Christ-likeness?

Sanctification—the process of becoming more like Christ—is a profound mystery: God alone causes the growth (1 Cor. 3.6-7), and yet Christians are commanded to pursue their own spiritual growth (Php. 2.13, 2 Pet. 3.18). How can that be? More than that, what are we supposed to do about it? The apostle Paul answers that question for us, but maybe not in a way we might expect.