Holier than thou basically means, in today's language, holier than you are. In other words, it means that when I am trying to make you a convert to Christianity, I would be above you because I am holy and you are not. But is this really a true statement and why is there a concern about a person who is sharing the Gospel being 'holier than thou'?
Well, the Gospel is composed of grace and truth. The truth is, the recipient of the Gospel is a lost person, far away from God. The truth is that all of us, not just hardened criminals or prostitutes, are steeped in sin, for sin is basically selfishness. The more selfish a person is, the less aware of God and their need of Him is there.
So, the recipients of the Gospel (which, hopefully is all of us!) are needy sinners needing a Savior and needing to be rescued from our sins. Salvation doesn't exist in people who do not see themselves as sinners, or people who think they are basically good, but need some help from God. I still personally think that a lot of 'Christians' are in this category, for, when I talk with many professing Christians, they are offended when talking about the 10 Commandments or sin, as if to be saying, 'how could you even think of me as a sinner?'.
But the problem with the phrase 'holier than thou' implies that the person sharing the Gospel (the Christian evangelist) is without sin. Somehow, this person thinks they have a special 'in' with God that others don't have. Basically, it is a deception of how serious their own sin is before God.
We can see the sins of others so much more clearly than we can see our own sins, and that is to our disadvantage (see Matthew 7:1-5). If we do see our sins, we tend to justify them (I'm that way because I am tired, or, I do that because everyone hates me). While we are learning to appreciate the grace of God and the power of the Blood of Christ, grace will be meaningless to us if we don't see the depth of our sin (Note: no person will actually see the depth of their sin to the degree of that depth, but we do need to see the seriousness of our sin instead of pretending it is not there).
The root sin of being 'holier than thou' is pride. The Bible has a lot to say about pride. You might even think that you don't have pride! That is the deception of it all, because pride will keep us away from God, and unappreciative of the Gospel as it applies to ourselves. We must apply the Gospel to our own hearts before we can minister it to others.
People who know the Lord Jesus Christ and are abiding in Him will bear the fruit of the Spirit in their lives, and this brings glory to God. If we try to evangelize in our own strength and wisdom, we will dishonor God, and we will be the focus of our evangelism instead of God. God is the One who saves people and works in their hearts. We are in danger if we are looking for people to be convinced or changed because of our evangelistic efforts. (Thinking we are adding brownie points or notches in our belts every time we share the Gospel or make a convert). We might live a long, long life, and perhaps will never see the fruit of our labors, but God is still at work and we need to be faithful in responding to the love of God that God has placed in our hearts.
The bottom line is, Christians have a bad reputation for being 'holier than thou'. No wonder people don't want to listen to us when we start to share the Gospel with them. They already know what is coming (or they think they do). We tend to be very judgmental, and God's word forbids that. God will judge people for their sins. Our job is simply to bring the Gospel to them in love so they can escape the wrath of God. It is not our job to change their hearts or minds. We present the truth in love, and stand up for the truth whenever it is being opposed, but if we misunderstand evangelism and how God wants us to carry out this work, we are going to cause a lot of damage to the cause of Christ, and we will repel people to the Gospel.
Let's take note on things we learn from the past. I saw a show on TV one time (I forgot to turn the TV off or change the channel) and on this show there was a Christian family who relocated to a primitive lifestyle (no electricity, or modern equipment) and the other family was totally worldly. The wives were swapped for a week (there was no immoral actions here that I noticed). Their basic jobs in their own homes were taken into the other's home. The amazing thing about this show was that at the end of the program, the Christian woman and the worldly woman (and their husbands) were at the table discussing the events and conclusions of the week. It was disappointing because the Christian woman was proud. While they were at the table, she asked the worldly woman why she (the worldly woman) was wearing a provocative dress. This is not how you handle people in the world. If you want to handle someone wearing provocative clothing, you either address them in private or leave it alone. I am not talking about someone who is involved in church and not addressing the situation. But this is not a question you ask someone who doesn't know the Lord yet. In fact, the worldly person could end up thinking that a good 'Christian' woman is one who doesn't dress in a provocative way, but that would be miscommunicating the Gospel message. (This is how moralists believe). Addressing the way a person dresses (when it is wrong) goes under the category of discipleship and accountability, not evangelism. Well, the worldly woman was the humble one and told the other woman that she actually enjoyed the things she learned from her, but you could tell that she was hurt (and confused) because of the dress question. I will say though, that in the end of the program, the narrator said that the Christian woman apologized a couple of weeks later.
I just think we need to be careful in how we treat outsiders. They are not in the light yet, and we can't expect them to act like they are. We can ask them questions in order for them to look at their own hearts, but to attack them for anything, will cause them to turn away from the Gospel, the church, or anything that has anything to do with the word 'Christian'. The key is humility, and the motive needs to be love. This is what we need to cultivate in our own hearts before trying to help others in seeing their own hearts.
"I am just one beggar telling other beggars where to find bread" D.T. Niles