John 3:36 Whoever believes in the Son has eternal life; whoever does not obey the Son shall not see life, but the wrath of God remains on him.
Even the demons believe that Jesus is God, but the implication here is that true belief requires obedience. We may believe and not obey, but this leads to the wrath of God on us.
This is a great verse to go to when someone says they are a Christian but they never go to church, never read the Bible, never pray and act just like the world. There is no obedience to point to, so where is the proof of life?
In love, we must be bold to call this to the attention of those we love who are not walking in obedience. This may quite possibly be the hardest, most loving conversation you can have with them, but how will they hear without a "preacher"? Inspect the fruit and then ask the question; "You say you're a Christian but it doesn't seem like you obey God's Word. I love you and don't want you to have God's wrath on you. Are you really a Christian"?
Lord give us opportunities and then give us the boldness to take the opportunities you give. We are weak and we often don't want to stir up conflict, but this is a conflict that we need to be willing to engage in, with Your help. May we love others enough to ask hard questions. Give us fruit in our asking that we might be encouraged to ask more, but not so much that we become proud. Thank you for allowing us to see our sin and turn toward You. May we want others to have the same joy as we have in You.