When I grew up we always wore our "Sunday best." This was a show of reverence for entering the Lord's House. We dress up to go to weddings, funerals, formal parties, etc so why not wear our best when we enter the Lord's House as a sign of respect and reverence?

That being said, this can also present a barrier to people attending a church because they don't have a sport coat or a tie, etc. Or maybe they are visitors in town and looking for a church to attend but just don't because they didn't bring their dress up clothes.

In the end, God only cares that we worship him above everything and everyone else. That personal relationship with Jesus Christ.......now that is the most important. If he leads you to wear your Sunday best then so be it. If he doesn't, so be it.