We are configured to the way of the world once we come into this lifetime. Our human configuration is actually the source of our sins. Effect of original sin. What we mean by "Christian struggle" is basically about us being torn between the configuration of the world, and the configuration of God's kingdom, in us. It is more than just about doing good and avoiding evil, of course doing good and avoiding evil is important, but our spiritual life goes beyond this simplistic meaning as how people outside the Church understand it.