First, it would probably be good to discuss modesty. Modesty, in many ways, is defined by the culture in which one lives. Now let me make it clear that I do not believe that culture allows us to transgress God's laws if our culture is accepting of some act or way of living if God has forbidden it. That being said, there is clear Biblical evidence, as well as logical conclusions, that what is modest can be greatly affected and shaped for the Christian by the culture in which they live. Consider I Corinthians 11:2-5;13-16 for a moment.
Now I commend you because you remember me in everything and maintain the traditions even as I delivered them to you. But I want you to understand that the head of every man is Christ, the head of a wife is her husband, and the head of Christ is God. Every man who prays or prophesies with his head covered dishonors his head, but every wife who prays or prophesies with her head uncovered dishonors her head, since it is the same as if her head were shaven...Judge for yourselves: is it proper for a wife to pray to God with her head uncovered? Does not nature itself teach you that if a man wears long hair it is a disgrace for him, but if a woman has long hair, it is her glory? For her hair is given to her for a covering. If anyone is inclined to be contentious, we have no such practice, nor do the churches of God.
Notice hear that Paul is discussing prayer, one way in which we can worship God, and in context is talking about a time in which they have gathered as an assembly. Paul talks about how it is not only shameful for a man who prays and prophecies have long hair, but how it is also shameful for a woman who has her head uncovered when she prays or prophecies, and is no different than her head being shaven. Paul mentions that even nature teaches that long hair on a man is shameful, but in what way? Is man inherently opposed to having long hair, while women are inherently opposed to having short or shaved hair? Not at all, rather, the word nature here refers to a learned behavior or way of life, one that was defined by their culture. Because of what it would lead others to think about them, there were some things they could not do because of society's disdain for them. Does our society view all long hair on men as shameful, or does long hair insinuate some sort of sinful lifestyle? How long is too long? What about short hair on women? Is it viewed with shame, or does it suggest something immoral? How short is too short?
We can also consider I Timothy 2:9, which addresses the appearance of women in a congregational worship setting.
I Timothy 2:9 likewise also that women should adorn themselves in respectable apparel, with modesty and self-control, not with braided hair and gold or pearls or costly attire,
Should we conclude from this if a woman today wears her hair in a fancy braid, wears any sort of jewelry, or costly attire (at what price does it become costly attire?) is in sin when she worships with other Christians? If so, then there is an extremely large group of women that need to be corrected! No, instead we see in two different epistles that how Christians were to dress were influenced and affected in many ways by the culture in which they live, and we can see this in practice still today. When I do mission work in Jamaica, there is a cultural dress that is very different from what I am used to, and if I wore what I might normally wear in America, I would stand out, maybe even be considered a show-off. In like manner, a friend and brother of mine who preaches in the Philippines described what they might normally wear, and it would be considered beyond casual in many American churches today.
Now there are passages within the Old Testament that refer to the topic of clothing while worshiping God, and while the Old Testament was "written for our learning," we must remember that it was to guide us to the new covenant. There is much within that old covenant that focuses on the outward, and ritual, and it is important to note that, but it is also important to note that these things were a shadow of the ethics and behavior of God's kingdom on earth, and so we much be very careful in picking and choosing what we pull from the old covenant as principles for better understanding the new. Did the priests under the old covenant have a certain garb? Certainly, though it is also the case that the average priest had a much more plain garment than the high priest, and that, according to Leviticus 16, when the high priest went behind the veil on the day of atonement, he too would have a much plainer garb than he would in his normal day to day duties, but is the principle in that to be that God's priests today need to have the best clothing by society's definition? I would not personally be quick to jump to that conclusion.
Other than those two passages we noticed above, I cannot find much of anything in the New Testament that is very specific on our outward appearance when it comes to worshiping God. That is not to say there aren't any, just that as I write this I am not aware of any others. There are a plethora of verses though that talk about the inward "dress" of man though. Other than noting that we should not go out publicly, and even in worship with other Christians, in a way that would cause society look at us in shame and to question our morality, God seems more concerned about the condition of our heart and mind when we come and worship Him.
I would imagine though that whenever this topic is discussed, people expect some sort of discussion on the typical suit and tie that many of the more conservative churches seem to expect. Should we simply rebel against this? Well, no, not if it will cause division and strife, and not if it will cause the brethren and/or the world to look on you with shame, or to question your morality. If I am preaching, there is a 99.9% chance that you will find me wearing a suit. Why? Because I feel it is the right garb for a preacher to wear? Not at all, but normally because it is what is expected and I do not wish for the focus to be on me, what I'm wearing, and why I might be wearing something unexpected.
At the same time though, we as Christians do not need to grab onto this particular trend for "worship wear," and hold on so tight that it becomes something we bind. And let us also be honest with the fact that even though we might often say we don't bind the issue of wearing some particular type of dress clothing to worship, that can often found that it is implicitly bound, or that we find ourselves like those in James 2 who begin to judge someone based on what they are wearing. We might find ourselves worrying so much about what someone is wearing, wondering if they didn't have anything better to give to God, or how we just saw them at a funeral in suit last week, yet for worship they wear jeans and a polo, that we end up compromising our ability to properly worship in the process.
What many fail to take note of is that America is currently in the middle of a generational change. We might notice it in the sense that we note all of the bad things that are happening, but in doing so we might fail to remember that generational, or cultural, change is not inherently bad, and even if many aspects of it are, it doesn't mean all of it is. The Millennial generation has recently surpassed the Baby Boomers for the largest generation in America. Baby Boomers are also at the point where they are getting much closer to retirement, if not already there, while Millennials are entering the work force, or may be at a point where they are taking many of the powerful and influential positions from the past few generations. That means that our culture is in somewhat of a flux right now. We've seen that that can bring about a lot of negative, and ungodly changes, but it also connects back to the principle of modesty we noted earlier.
Because we are in a flux, it can hard to always pinpoint the cultural side of modesty. We have many Baby Boomers still in positions of influence and power, speaking of a secular sense, that hold on to many of their generations cultural concepts of modesty and what is appropriate. At the same time, we have many Millennials who are bringing in what their culture deems as modest and appropriate, and so we have a good bit of friction and strife that may come up because of it, and the problem is that this friction and strife is not always kept out of the Lord's church. We have many well established brethren from the strong Baby Boomer generation, and at the same time have a great number of Millennial brethren that are reaching the point where they are expected to help lead the congregations, and both have scruples and aspects of culturally based modesty that they hold onto, and so friction and strife occurs, and both sides grab on tightly to their scruples, and their generational culture, and hold on tight, refusing to budge, and at the same time questioning the love that the other group has for the Lord, how devoted are the really if they would act or appear in such a way, how they are trying to bind what is not bound or lose what is not loosed. Consider this quote from C.S. Lewis on the topic of modest clothing in the midst of a cultural and generational shift:
"While this confusion lasts I think that old, or old-fashioned, people should be very careful not to assume that young or 'emancipated' people are corrupt whenever they are (by the old standard) improper; and, in return, the young people should not call their elders prudes or puritans because they do not easily adopt the new standard. A real desire to believe all the good you can of others and to make others as comfortable as you can will solve most of the problems."
If we fail to do have the understanding and Biblical attitude towards cultural bound modesty what is the result? Well ultimately we get so caught up in these little cultural battles over things that are not as important as either side may make them out to be, and were never going to be permanent in the first place, as change in culture will always happen, that we lose the opportunity to be a light to the world. We get so caught up in nitpicking little things that are more of a matter of the culture in which we grew up than an actual Bible command or desire of God, that we lose our ability to be effective in teaching people that God's church is about how groups of people can all find common ground despite generational or cultural differences, and how God's kingdom focuses on what is eternal rather than what is temporary. And the problem is that both sides of this generation change are to blame.
Of course, I also have to ask the question of consistency in how we practice these issues. Many brethren have asked why men might wear suits to the morning worship service of a congregation, but just jeans and a casual button up at night, and while I might disagree with the conclusion they have about what to wear, their question is no doubt a valid one. What is the difference between the two services one might attend on a Sunday? But what about other times where the congregation worships together in some fashion? What about Wednesday night when we have singing, praying, and teaching? Should our Sunday garb not be the same, or does the fact that we collect an offering and partake in the Lord's Supper on Sunday change what we are expected to wear? What about a youth devotional? What if I am worshiping alone, singing songs of praise to God? If God expects me to appear a certain way when with the saints, is it different if I'm alone? These are questions that BOTH sides of the issue need to consider if they are going to take the time to debate and discuss the issue to any real depth.
To make a short conclusion to a rather lengthy post, maybe it would better for us to stop nit-picking a number of different issues that are going to end up being, Biblically speaking, affected a great deal by the cultural stance on things, and focus on perfecting unity with one another despite differences, all while being an example to the world what the church is supposed to be. Does that mean I have the answer to the question in the title? Not entirely. I do believe the Millennial generation still has a sense of respect of reverence for what they wear outwardly when it comes to worshiping God though it might not match up to the older standard, just as much as I believe that the older standard holds a greatly needed respect for the act of coming before God in worship and praise that many Millennials today need to learn from and practice as well. Might there be a middle, and hopefully Biblical, ground for us all to stand on?