“Your attitude should be the same as that of Jesus Christ.” – Philippians 2:5
“Anyone who claims to live in him must walk as Jesus did.” – 1 John 2:6
If someone says they are a Christian, you get to judge them inside and out.
Inwardly, they should have the attitude of Jesus.
Outwardly, they should have the “walk” of Jesus.
These are the inner and outer standards upon which all of us who call ourselves Christians measure ourselves. (Not in order to get eternal security, by the way, which is a free gift of love from God, but as the evidence that we have received this free gift…for they are earth-bound results of belief in Jesus.)
And while the Bible makes these two things clear, it also makes it clear that there is a transformational process involved in the becoming like Jesus (Romans 12:2, for example).
Combine these two things, and the true standard that you can use to judge if someone is a Christian is whether or not that someone is actively involved in his or her own transformation into the image of Christ.
If you asked them, they would be able to tell you…
…that they are becoming more like Christ.
…that they are not finished becoming more like Christ.
…how they are becoming more like Christ.
…what old attitudes and actions they had that weren’t like Christ.
…what current attitudes and actions they have that aren’t like Christ.
…what new attitudes and actions they have acquired that are like Christ.
…what attitudes and actions they lack that are like Christ.
…what they participated in, in order to transform into Christ likeness.
…what they are currently participating in, in order to continue transforming into Christ likeness.
So, if you ask them these questions, and they can’t answer (now, give ‘em a minute, because not many ask them to articulate these things), you are free to doubt that they are Christians.
No matter what they say.
Jesus, his attitude and his ways, are the standard of judgment.