This is one of those passages that is straightforward and crystal clear. If someone is not a fully devoted follower of Jesus Christ, they value different things than someone who is. They spend their time differently. Quite understandably, they make very different decisions.
And so, for the Christian who is serious about their relationship with Christ, there is no “going along with the crowd.” It only makes sense that our lives would look very different from the lives of the world around us. If they don’t, something is wrong.
I love how Eugene Peterson translates verses 20-24:
But that [following the crowd] is no life for you. You learned Christ! My assumption is that you have paid careful attention to him, been well instructed in the truth precisely as we have it in Jesus. Since, then, we do not have the excuse of ignorance, everything—and I do mean everything—connected with that old way of life has to go. It's rotten through and through. Get rid of it! And then take on an entirely new way of life—a God-fashioned life, a life renewed from the inside and working itself into your conduct as God accurately reproduces his character in you.
The following verses give very practical ways we are to put on this new life in Christ. Speak only the truth. Care enough to be angry, but without sin (I think this probably has a lot to do with how attached our anger is to our ego.) Have integrity. Work in order to share, not just for personal gain. Speak only gracious words that build others up. Don’t break God’s heart. Be kind, tender-hearted, forgiving.
Any one of these is potentially revolutionary. Any one of these can change a life and cause it to stand out in bold relief from the world around us. These are the kind of things that happen when a person really does pay attention to Jesus Christ.
This is what it means to be faithful to him.