Dojo Kun - literal translation means "training hall rules". There are five main rules that serve as guiding principles for all who train in the dojo. Although they are usually listed in a set order, no one rule is more important than any other. To emphasise this all five are prefixed with hitotsu and end with koto, which together mean "one point".
Hitotsu! Makato no michi o mamoru koto.
I urge you to research the meaning of the dojo kun and to draw your own conclusions as to the true meaning of each rule (start here at Wikipedia). Then, once you've done that, set upon Gichin Funakoshi's 20 Precepts (Niju Kun) and see what you make of them.
Here's my take on Be Faithful. First of all, we need to ask, "be faithful to whom or what?" Are we able to interchange the term "be loyal" and still achieve the same outcome? Does one stand to be accused of heresy if we fail to observe this rule and consider other art forms worthy of our attention? What we proudly refer to as Shotokan karate, Bruce Lee would have categorized as part of the "classical mess".
I think we need to understand whether this rule is specific to Shotokan, or to Bushido, or to Funakoshi, or to our own Sensei perhaps. Or maybe it's more generic than that. Maybe it's referring to each of us as individuals. Maybe Funakoshi was tasking us with being faithful to ourselves as individuals. Whether we are in the dojo practicing karate or outside practicing life!
There are two quotes that have served me well for many years now. First, inscribed in the forecourt of the ancient Greek Temple of Apollo at Delphi, "Know thyself". Second, from Shakespeare's Hamlet, "To thine own self be true." Translating these into modern day English and combining the two, we can arrive at, "First, know (understand) your "self", then, once you have, be true to your "self". Which, after all is said and done, is easier said than done. And, as Bruce Lee said, "to express oneself honestly, not lying to oneself ... is very hard to do."
Bear in mind that this is not a one-off exercise performed at an early age and set in stone for life. It's a continual process as we wade through life learning and growing with each and every passing day. Strive to be the best version of you that you can possibly be and you can't go too far wrong. The Dalai Lama offers some simple guidance on how to achieve this, "Be nice person." It really is that simple.
Maybe we'll never know exactly what Gichin Funakoshi intended when he penned this two-word rule that has spawned many attempts at a plausible explanation. Perhaps he intended it to be deliberately vague, obtuse and somewhat ambiguous. I think starting with being faithful (or loyal) to your own self is a good place to start because we probably can't be faithful or loyal to anyone or anything else if we can't first afford ourselves the same grace.
Karate-dō, like any other art form, is much bigger than any single individual. It doesn't have intellectual property rights attached to it, or at least, it shouldn't have ... because that would be a business venture! Karate is for all people to study and practice as a matter of choice. We adhere to standards and rules because that's what differentiates Shotokan from other styles of karate, and karate from other forms of martial arts. So, you can choose to ignore the dojo kun if you so wish, but just be aware that if you do, your welcome in most dojo's would be short-lived.