Jude 1:3

Beloved, while I was making every effort to write you about our common salvation, I was compelled to write you (urgently) appealing that you fight strenuously for (the defense of) the faith which was once for all handed down to the saints (the faith that is the sum of Christian belief that was given verbally to believers).

As Christians, we must fight to keep our faith from being tainted by worldly influences and corruption. It matters what we watch and listen to because of its impact on our thinking.  Where we concentrate our time will have the most influence. Our faith will stay strong if we focus our time on the word.