Let's go back to a verse we looked at a week ago. Keep thy heart with all diligence; for out of it are the issues of life. (Proverbs 4:23)
The key principle in this passage is if the heart is so important – remember it determines the course we take, decisions we make, etc. – then we ought to pay careful attention to protect it. We ought to diligently keep it.
It is our responsibility to vigilantly guard our hearts against any ungodly influence, knowing that what we allow in our hearts will work it's way out in our lives. This includes the company we keep, the music we listen to, the shows and movies we watch, the books or magazines we read, the internet sites we visit, the places we go, the activities we involve ourselves in, etc.
1 Corinthians 15:33 says, Be not deceived; evil communications corrupt good manners. So often, we allow ourselves to be deceived into thinking that subjecting ourselves to things we know we shouldn't subject ourselves to won't hurt us. That because we know the Bible, or because we've memorized verses, or because we have a Christian home, or because we attend a Bible-believing church, we're strong enough to handle it.
But God said not to be deceived. If we open our eyes, open our ears, open our minds to the world, the flesh, and the devil, we will be corrupted. If we give place to the devil, the devil is going to take that place (Ephesians 4:27).
Wherefore take unto you the whole armour of God, that ye may be able to withstand in the evil day, and having done all, to stand. Stand therefore, having your loins girt about with truth, and having on the breastplate of righteousness. (Ephesians 6:12-13)
And lead us not into temptation, but deliver us from evil: For thine is the kingdom, and the power, and the glory, for ever. Amen. (Matthew 6:13)