This is a strong rebuke. Remember, James is addressing the church. Not unbelievers. So when he calls them adulterers, he means they are being unfaithful to God. As the bride of Christ. This is spiritual adultery, not physical adultery. By being friends with the world, the church is being unfaithful to God. What does it mean to be friends with the world? In James 1:27, we learned that the world consists of people who are rebellious against God. It is the evil world system. It is a way of thinking that denies God. A lot of the world’s philosophies and ideologies and what they offer may look attractive and appealing but they are full of deception. They are evil, harmful and satanic. They ultimately bring ruin to our lives. Satan uses the world system to entice the flesh. Look at 1 John 2:15-16. The eyes in particular are a strategic avenue to incite wrong desires. The emptiness of the world brings disillusionment, sadness, pain, isolation, suicide. I worry about those that I know that are Christians who don’t come to church anymore. Are they being pulled back into the world’s system of thinking and living? Are they friends of the world? When we commit spiritual adultery by being friends with the world, it makes God jealous.
James 4:4, 1 John 2:15-16