Are you a Christian?

This is a question many Christians would never think to ask someone else. But is that a good thing? Is this question really so unkind as some may think? If it sounds so unkind to ask this question, why do Jesus, Paul, Peter, and John all talk about the difference between a true brother and a false brother (Matt. 18; 1 Cor. 5; all of Galatians; 1 Pet. 2 and 3; Rev. 1-3)? So if a professing Christian consistently does things and says things that are out of step with the characteristics of a Christian, what are we to think?

Having recently read the 18th century theological (giant) Jonathan Edwards on a similar topic, my thinking has been helped here. Check out what President Edwards says,

"I know there is a great aptness in men who suppose they have had some experience of the power of religion, to think themselves sufficient to discern and determine the state of others by a little conversation with them; and experience has taught me that this is an error. I once did not imagine that the heart of man had been so unsearchable as it is. I am less charitable, and less uncharitable than once I was." (Distinguishing Marks of a Work of the Spirit of God, emphasis added)

This is instructive for me because I am very quick to label an inconsistent Christian as a non-Christian. I think this is often arrogant and uncharitable on my part. Edwards seems to indicate in the context that we should truly leave to God what is his in determining someone's spiritual state. In other words, the Living God is the one who sees the heart; we do not decide on their heart. (However, as a baptist I would say much care should be taken with this sort of question in a church membership process.) Pray that I will be charitable and kind!

Any thoughts? Things to add? Am I just plain crazy?