vplee any of us are capable of anything, even as Christians, and behaving in a way (an un-Christian like way) such that it can appear that we are or are not Christians or Christ like. Over all I believe Christ instructs us not to JUDGE one another or set in Judgement of one another and I fully believe the purpose of this is as much for our own selves as it is not to be destructive of our own witness or destructive of others around us. Often when a person judges another it is out of a feeling of superiority and infallibility in that the person feels they are superior or more holy than another and they stand above the reproach of anyone else. Many that judge others also do not see that it harms their ability to witness of Christ and hurts their personal testimony and builds walls rather than opportunities.
I also believe though that the emphasis, about Judging, applies more to Christians judging non-Christians than Christians judging other Christians actions to see if they are in accordance with God's/Christ's instructions as how we are to relate with one another, in Love .. etc such as instructed in examples like with Romans 14 when it comes to differences in personal belief among fellow Christians, in matters where two see things two different ways or in matters of interpretation variances of minor doctrinal issues.
That said I also believe that, as Christians, we are to be fruit inspectors, so to say, that we are to test what others around us are saying and teaching. We can look at the lives and the indicators associated with those around us who claim Christ and claim to be teaching His word and claiming some kind of authority to teach and instruct and correct. We are not, as Christians, to just accept someone's word that they are legit and that their motives are noble and honest and not prideful.
We cannot view into each other's hearts and minds and know surely that what is there is genuine but what we can do is observe if the conduct and actions of those who claim the name of Christ correspond to that which proceeds from and comes from the possession and the presence of God's Holy Spirit, also known as "The Fruits of the Holy Spirit".
Consider the following:
Galatians 5:22-25
New King James Version (NKJV)
22 But the fruit of the Spirit is love, joy, peace, longsuffering, kindness, goodness, faithfulness, 23 gentleness, self-control. Against such there is no law. 24 And those who are Christ’s have crucified the flesh with its passions and desires. 25 If we live in the Spirit, let us also walk in the Spirit.
This doesn't mean that all Christians will show these fruits in their lives and actions but the thrust of vs 25 is to command and suggest that we, as Christians, with a concern for Christ SHOULD WALK in the Spirit. If a person IS Saved, and IS honestly walking with Christ and in God's Will then there is no reason or hindrance that would prevent these very fruits from being openly visible and demonstrative to all those around that person and that interact with that person.
So if there is any concern or question as to if a person is walking in God's Will and functioning as a Christian or mimicking Christ then each of these Fruits of the Spirit should be most evident and come through in not only their interactions and writings with others but their life in general and are an open and public testimony to those around that Christian that there is something special and meritorious about that person that is exceptional and supernatural in that they are not acting as normal humans are, not reacting as normal humans are in and with anger, malice, or any of the opposites of the Fruits that naturally come from God's Holy Spirit's presence.
Again, absence of these Fruits doesn't mean that a person is lost or that we are to judge that they are lost but it also could mean that that, professed, Christian is NOT WALKING in the light of Christ and not walking with and in the Holy Spirit but possibly attempting to do things themselves apart or away from the Holy Spirit. In other words not being responsive to the Spirit's direction but setting of on a course they determine is right and the best, potentially out of ignorance of the word or pride itself for any Christian is also just as capable and able to sin and fail as anyone else including doing the same as those that do not know Christ. Judging another therefore is not to our advantage other than when to determine if they are acting in the Will of God and in accordance with Scriptures and Christ Directions.
Just a few thoughts to consider for motivation is very difficult to determine and often the best course of action is just to Love one another, even when love is not warranted, and pray that God's Spirit will minister unto those who harm us and who offend us and pray that God, through His Holy Spirit maintain us in His Will and show Christ (Love and testimony) through our own lives and responses and reactions with others. That is my own two cents worth of suggestion and comment.