Two passages in the Epistles give instructions on our attitude to clothes, one in 1 Timothy, the other in James. 

I desire ... that women should adorn themselves modestly and sensibly in seemly apparel, not with braided hair or gold or pearls or costly attire but by good deeds, as befits women who profess religion.           (1 Timothy 2:9-10)

In Greek and Roman society expensive clothes and elaborate, time-consuming hair-styles, decorated with jewellery, were a means not only of making an impression on others but also of demonstrating the wealth and social class of the woman and her family.  At various periods of history,  men have likewise dressed to impress. Clothes today, while not necessarily extravagant or expensive, still tend to indicate something about status in society. The principle behind Paul’s comments above is that worldly estimates should have no place amongst believers. It is quality of character that is important, resulting in good deeds.  Seeking to impress by dressing up is not appropriate Christian conduct.  While it is common practice for most of us to wear our best clothes when attending the meeting on Sunday, the New Testament does not supply support for this approach.  Nor does it justify the idea that some meetings of the ecclesia are informal (and casual clothes can be worn), while others like the Breaking of Bread are formal, and we should therefore dress up.  Sometimes 1 Corinthians 14:40 is used to argue for formal wear (“... all things should be done decently and in order”) but this verse is not talking about clothes but about avoiding disruptive behaviour at meetings.

It is easy to allow us to be influenced into judging people’s characters by what they wear.  Recently a young man tried this out by visiting some of the Lutheran churches in America. He dressed cleanly but informally in a sweat shirt and jeans, and found himself either ignored by the ushers or shown to the back row! James gives a warning about doing this:

My brethren, show no partiality as you hold the faith of our Lord Jesus Christ, the Lord of glory.  For if a man with gold rings and in fine clothing comes into your assembly, and a poor man in shabby clothing comes in, and you pay attention to the one who wears the fine clothing and say, “Have a seat here,  please,” while you say to the poor man, “Stand there,” or, “Sit at my feet,” have you not made distinctions among yourselves, and become judges with evil thought? .... If you really fulfil the royal law, according to the scripture, “You shall love your neighbour as yourself,” you do well.  But if you show partiality, you commit sin....               (James 2:1-9)

Since people in the world do tend to judge by appearances, we should take care not to give the wrong impression.  The wrong impression can be given if we all look expensively dressed, or if we all look shabbily dressed! Since the Gospel message is relevant to all, it is appropriate that we should dress in clothes normal to each of us, not attempting to have any sort of universal standard dress-style or insisting on it for others.  Fashions in dress change; what one generation likes, another dislikes.  For example, several decades ago people tended to disapprove of women wearing trousers;  nowadays, it is generally accepted and young people of both sexes frequently wear jeans.  There is nothing wrong or unbiblical in this.  Sometimes the prohibition in Deuteronomy is quoted:

A woman shall not wear anything that pertains to a man, nor shall a man put on a woman’s garment;  for whoever does these things is an abomination to the LORD your God.                                                       (Deuteronomy 22:5)

This does not refer to clothing which is normally accepted by society as applicable to both sexes.  The context in Deuteronomy is not explained, but is likely to be a warning against the immoral practices of surrounding nations. 

Believers in Christ should not seek to follow the newest in fashion, nor deliberately trail a long way behind (which simply means following the newest fashion of several decades ago).  We should be different on issues that matter – morality, lifestyle, belief.  The words of Jesus are relevant. 

You cannot serve God and mammon.  Therefore I tell you, do not be anxious about your life, what you shall eat or what you shall drink, nor about your body, what you shall put on.  Is not life more than food, and the body more than clothing? ... why are you anxious about clothing? ... if God so clothes the grass of the field, ... will he not much more clothe you, O men of little faith?  Therefore do not be anxious, saying, “What shall we eat?” or “What shall we drink?” or “What shall we wear?”  For the Gentiles seek all these things; and your heavenly Father knows that you need them all.  But seek first his kingdom and his righteousness, and all these things shall be yours as well.                                                               (Matthew 6:24-33)

In these words Jesus challenges each of us on our modern-day materialism.  When most of us are so well supplied with this world’s goods, this passage makes uncomfortable reading.  The context contrasts a life devoted to material enrichment with the way of Jesus which is to seek primarily to live under God’s standards in the pursuit of goodness.  We should be grateful to God for all the good things we have received but we need to take care that these do not assume a wrongly important part in our lives.