You need to find joy in the right things. When we mind earthly things, our greatest intensity is toward earthly not spiritual things. Compare this with Philippians 3:16, instead of minding the same things as Paul, and those maturing in Christ, we have our own agenda, the same as the world’s, the same as we were before we supposedly forsook all for Christ.
Where do your passions lie? God will reveal if you are passionate about the wrong things, and He will do so in community. In the context of this passage, Paul is saying let’s all be passionate about the same things, growing in the knowledge of Christ, and if anyone isn’t God will reveal this, and He does it in the context of community, so follow those who are pressing on and make sure you follow what you already know to do. We also need to watch out, there are some who are passionate about earthly things first and foremost.
We’ll use an obvious example here. Considering how important and necessary money is, it can easily be perverted and become our passion more so than God, and we won’t give up our habits. Think about passages such as James 4:13-16 / Matthew 6:19-21 / Luke 12:16-21; wealth is not wrong but is it controlling you? Are all decisions based upon its production and protection, the “get it or keep it” idea being the most important thing to you (Colossians 3:1-3)?
The opposite of joy in a sense is lust. If I have joy in God I can wait on His plan and timing, even considering my sanctification. Joy is patient, and impatience is pride. Pride leads to lust, which says I deserve it now, or why do I have to wait, or why do I have to deal with this situation, or why am I here? Lust is “I want it my way and in my time, and that time is now”. It wants to go outside God's guidelines to find satisfaction.
Paul says these persons who are like this are enemies and their desire is to find joy in whatever way they deem necessary. They will not mature and they will do it the way they want to. They will not follow others as a pattern, and they think they know better, but they are wrong. They think they have found easy street, a better way, a Christian life and afterlife without a true Christian testimony. They might think they are covered by Christ’s blood, but they are only filling their veins with the virus of vanity.