Knowing someone is a Christian does not mean you know where they stand with Yahweh. It simply means that they identify with the Church, or their parent's faith, or some vague ceremonies of which they may be aware. There may be 2.2 billion people on this planet who identify as Christian but it does not mean they are followers of Jesus.
Jesus and the apostles told us what it looks like to be filled by the Spirit of God, because without the Spirit we will not look like Jesus. This only works when we do exactly what Jesus said, "Say no to yourself, take up your cross daily and follow me".
What does it look like to be a follower of Jesus? All kinds of ways but here is one sign post you should see in yourself:
Instead of each person watching out for their own good, watch out for what is better for others. (Philippians 2:4)
This cannot happen unless you have turned yourself to walk like Jesus, in the power of the Spirit. This can only happen in you when you have decided to love God with all your being and to love your neighbour as yourself. When those are the precepts that you are determined to govern your life, then the Spirit is able to transform your heart to be a vessel of Jesus' love. As a vessel, your entire desire will be to love as Jesus loved.
How did Jesus love? By serving others. By giving all he had to give. By dying for sinners. By making everyone else more important than himself. And he told us to love each other as he loved us.
How do we love? This is an excellent question in this age of "love yourself". Do we believe what Jesus said? Do we trust him? Do we expect Father to look after us while we seek to see his Kingdom here, to have it done here as it is in heaven? That is what Jesus told us, that dad will look after us while we are busy with the Kingdom. It is a Kingdom matter to put everyone ahead of yourself.
It is by these signs that we know we are really disciples of Jesus. Anyone can call themselves anything, but we are known by the fruit that is produced in us, by our words and actions. Are we so convinced of Jesus' love that we can put our own needs aside to look after the people he loves; the lost of this world?