As new creatures living under the authority of Christ, believers have been rescued from the corruption of sin and set aside for righteousness (cf. Leviticus 20:26). Our new nature is no longer compatible with the world—the transforming work of salvation makes us aliens in a lost and dying society, at odds with the very things we formerly loved. The lordship of Christ forces us to denounce the impurity and worldliness that once informed our character and occupied our hearts.
Ephesians 5:3-4 has excellent words in this regard:
Immorality or any impurity or greed must not even be named among you, as is proper among saints; and there must be no filthiness and silly talk, or coarse jesting, which are not fitting, but rather giving of thanks.
Those two verses alone rule out much of what passes as entertainment in our world today—sexual immorality and impurity, dirty jokes and silly talk, and anything that promotes greed or undermines the giving of thanks. In fact, that list is a pretty good summary of what is wrong with much of contemporary American media.
Movies, for example, are usually rated according to language, violence, sexual content, and thematic elements. Many of them are not just non-Christian, they are anti-Christian. I don’t mean that they openly attack the Christian faith. But at least in some cases they might as well. They employ filthy language and lewd humor (Colossians 3:8, Titus 2:6-8); they glorify violence rather than peace (Titus 1:7, 1 John 4:7-8); they glamorize lust and immorality rather than holiness (1 Thessalonians 4:3-5, 1 Peter 1:16); they instill feelings of discontentment and desire rather than thankfulness (Ephesians 5:20, 1 Timothy 6:6); and they promote worldviews that are antithetical to biblical Christianity (2 Corinthians 10:5).
Does that mean a Christian should never watch movies? Not necessarily. But we must be discriminating about the things we allow into our minds. We are called to renew our minds (Romans 12:2, Ephesians 4:23, Colossians 3:16). When we continually fill our minds with the filth of this world, we do ourselves a great spiritual disservice.