Human tendency is to examine others to see if they are in the faith. Problem with that is that first, we don't know the whole story. We have no idea what God is doing within others. We have no idea what God has called them to do, what God is saying to them, even where they are at in life. And second, it's none of our business and we should stick to what we need to stick to -- examining ourselves.
How do we know if we are in the faith? If we are living our faith out or if it is just lip service? We will know by how we act, how we think. Galatians 5 is a good one to read about flesh deeds and spirit fruit. Check it out here:
If you catch yourself reacting in anger, jealousy, frustration, striving, pride -- ah, I'll just copy and paste a few verses from Galatians 5. They are really good. I'm using the The Message Bible here:
The first part of those verses say it all -- when we are trying to get our own way. If we are doing that we aren't doing it God's way. Even if we are Believers, we still have to deal with our flesh on a day-to-day basis. We can be super spiritual giants one day and the next fall into a bunch of fleshly behavior and thinking. We need to be aware of ourselves. We need to live intentionally. We need to catch ourselves falling back into this bad behavior and go to God and let Him get you back where you need to be. We are to be free from our flesh. Living in the flesh stinks: no peace, no joy, nothing good.
"But fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, gentleness, self-control" Galatians 5:22-23a