First, there is the simple fact that the way we dress for an event is an expression of our attitude toward and understanding of the event. We all know this intuitively. When we have a job interview we dress well, groom ourselves nicely, straighten ties, and iron blouses. When a woman gets married she spends a great deal of time trying on and picking out the perfect white wedding dress. Similarly, the groom wears a suit or tuxedo as an expression of the fact that this is an important occasion and that he is presenting himself to his bride in a formal and sacrosanct manner. Soldiers wear fatigues, policemen wear uniforms, doctors wear white coats. All of this is to symbolize the importance of what we are going to do, or to mark us out as those doing one thing (and not another). When a policeman dons his uniform it lets everyone know that he is policing. When a young man spiffs himself up for a date it is to let the girl know that he views this as a special occasion, calling for extra attention to his appearance. All of this is to say that our manner of dress is an expression of our attitudes and beliefs about what we are doing. Even casual dress expresses something. It indicates that this is not a special occasion, but time for rest, relaxation, maybe some work around the house.
But this line of reasoning begs another set of questions. Often we hear that church is different. After all, man looks on the outward appearance but God looks on the heart. (By the way, that reference comes from I Samuel 16 where God is speaking to Samuel about which of Jesse's sons to anoint king, but interestingly a few verses later when David is found to be the one, we are told that David "was ruddy and had beautiful eyes and was handsome." So it behooves us not to get carried away.) Yet it is precisely because the outward appearance (so far as it is in our control) is an expression of the heart, that the way we present ourselves for worship is significant. As I said above, if a young man's heart yearns for a young woman, that will express itself in the way he presents himself to her. If my heart desires a job, that desire will take outward form in presenting myself as clean and well kept at an interview. This gets at the root issue, that often behind these kinds of arguments lies a kind of dualism. It is often supposed that because God is concerned with the issues of the heart (which he surely is!), he must not give a wit about outward forms or appearances. But this is not the Christian view. Indeed, are we to suppose that the God who gave woman beautiful hair for her glory (I Cor 11), who wrote Song of Solomon, who created the majestic oak and the dainty flower, raindrops and snowflakes, lions and toucans, is not concerned with outward forms? I demur.
No, God looks for beauty on the inside and the outside. In fact a better term than beauty would be glory. God likes glory. When the Spirit-Cloud hovered over the unformed creation it was as a glory cloud of light, just as when he appeared to our forefathers in the wilderness. And that glory overflowed, as it were, into creation, charging the world with an almost electric glory of it's own. And from that time forth God has charged man with the task of imitating him in glorifying the world. Adam's work was not for its own sake but that he might transform God's good creation from glory to glory.
This is why I believe that so many reformed err in their view that churches ought to be plain and unadorned. It is not only in creation that God has displayed his predilection for beauty. When God calls his people to form a place of worship what kind of place is it? Well, if nothing else we must say that it is a space charged with glory that was meant to house the very Shekinah glory of God himself. Think of the tabernacle with its finely woven tapestries, gold overlays, silver overlays, bronze overlays, filigrees of pomegranate and bells, candles, incense, etc. Indeed anyone who has read the pentateuch can't help but be overwhelmed by the level of detail and repetition that emphasize all the glorious intricacies of the tabernacle. And yet, such was not sufficient. Illustrating the progression from glory to glory, when God's people settle down with a King he calls for an even more glorious abode, a temple, to be surrounded by the glorious music and choirs that David had instituted a generation before. We could go on, but you get the point.
Yes, some might say, but that was the Old Testament. The idea being that in the epochs prior to Jesus coming God was concerned with such outward forms, but now, in the New Covenant all is inward and a matter of the heart. Not so. God has always been concerned with the heart, just read the minor prophets. But it was Jesus who said to clean the inside of the cup, because the outside doesn't really matter... Oh wait, that's not right. No, he said to clean the inside of the cup and then the outside would be clean as well (Matt 23.26). Which is to say, the outward is an expression of the inward.
Or we could turn to the Revelation given to St. John, and the worship described therein. While the book is of course highly symbolic, the descriptions of worship therein go into great detail about appearances. Lots of pure white, and beauty. And who is described as being pure white most especially? The Bride of Christ, the Church. No spots or wrinkles to be found.
Lest we get too far afield though, let's return to the question at hand. Is it appropriate for pastors and church leaders to encourage their congregants to 'don their best' for gathered worship on Sunday morning? Well, a few caveats. One, it is not necessarily our "best" that is called for in a culture where that might mean first, that some are dressed in far more elaborate and costly clothing than others and second, that some are wearing tuxedos to worship. Again, appropriateness is the question. Gathered worship is indeed a special time, and we do of course come into the presence of the most venerable of all hosts. However, it is also a regular gathering. We come each week, and it is to a meal that we are invited. Indeed it is to a feast, where, after appropriate peacemakings and reconciliations are accomplished we are invited to relax and to rest at table with our Host, who is after all, family.
So, if 'our best' means a tuxedo, or a wedding dress, no, we should not be encouraged to wear that. Nor should we even if we want to. Ostentation is not welcomed at the Lord's table (I Cor 11). But ought we 'dress up'? Yes. We ought to make our appearance and our dress fit the occasion. We have been invited to a feast with the King. Nevermind that the King is our Father, this is a semi-formal occasion and one for which we ought to prepare ourselves appropriately.
This does not, by the way, exclude the poor or those who are less fashion conscious. No one is suggesting that the price of one's clothes ought to make a wit of difference, or that there is some sort of minimum threshold of hoity-toityness that must be met. In our contexts the vast majority of people own more than one set of clothes, and among those clothes have those that are considered the nicer ones. And even if that were not the case, we all have ways that we present ourselves when we want to look nice. We fix our hair with a little more care, we trim our beards or tuck in our shirts. We all do it a little differently. And in deference to those taken issue with before it is true that God looks on the heart. It is not a pastor's place to judge whether a particular congregant is sufficiently dressed-up for worship (barring extreme examples), but God knows the heart and appreciates our efforts to present ourselves in a manner in keeping with our love and respect for him, not to speak of our brothers and sisters. It is pleasant to dwell in the company of others who have all put in a bit of extra effort in preparation for joining us in worship.
And that is what it's all about. Glory, while it can refer to weight and those things which overwhelm, also carries with it a sense of pleasantness. There is a subtle glory not far removed from sheer pleasantness in the little dainties carved into every doorframe and windowsill of a medieval cathedral. There is a glory that is pleasantness to be found in a home decorated with wreaths and tablecloths and knick-knacks appropriate to the season. And there is a glory-pleasantness in a congregation who has outfitted themselves with their 'nice things' and come together to worship and feast with the triune God.