Warning -- post Yom Kippur/religious post. If you are waiting for me to resume being secularly stupid, please continue to hold.
Each year at this time, I see the same claim made all over the place, that Yom Kippur is the "holiest day of the year" in the Jewish calendar. I chafe at this because it begs so many questions and is answered in a number of ways. Here's a basic ides -- the "holy" status of a day is, according to some, reflected in the number of people called to read (or have read on their behalf) a section of the day's assigned Torah reading. A weekday has 3 people. The new month has 4. Holidays have five. Yom Kippur has 6 and EVERY SABBATH has 7. So, in that sense, Yom Kippur is "less" holy than every sabbath in the year. So, clearly, the claim that it is the "holiest" day is arguable at the least.
What, though, is at the heart of this uncertainty? I believe that the answer is that we don't know what we are asking when we think we are presenting the answer. What does "holy" mean that we can assign levels of it to a day or a person? In English, the word "holy" means "sacred" (which tells us nothing...synonyms make terrible definitions) or "dedicated to God." That's somewhat better but it still clears nothing up as all holidays and sabbaths (and a host of other things) are dedicated to God.
So I figure to look at this through the lens of the Hebrew. The word in question is "kodesh" (yes, I know that real transliterationists will insist on my using Q, but I'm using K, K? K). That word does mean "sacred" but it also means (and you can look at Klein's Etymological Dictionary for confirmation, words like "forbidden," "purified" and "separated." So now we have a new angle to look at -- the "holiness" quotient of a day has to do with its being separated from other days. But how is a day, or anything else, set aside? The word "forbidden" gives us a clue. Something is set aside by the imposition of restrictions on it, showing us how its use is limited to sacred functions. Some of this is hinted here but I don't think it goes far enough, and I thought of it independently, so there.
As Jews, we often make blessings and in those blessings we acknowledge that God is the king of the universe who "made us holy through his commandments." Now, what does that mean? Well, to me, and in the mood I'm in, it means that we are set aside from others because we are limited in our behavior, controlled by a set of laws and commandments that restrict us to a particular path connected to God. The more laws we have, the more we become a "holy nation" because the more restricted we are! Now wait, you say, many of those laws don't tell you what you can't do -- they tell you what you must do, so how is that a restriction? Simply put, they tell us what we are required, BY THOSE LAWS, to do. That is its own restriction, even in a positive sense. So the more behaviors we are commanded TO DO, the more laws we have to follow in order to do them -- restrictions on behavior. Yom Kippur has a whole mess of laws and behaviors specific to its ritual practice (including the High Priest's entrance into the Holy of Holies, the kodesh kodashim, the most restricted place in Judaism).
I have to test this theory -- so I look at other uses of the word. The K-D-Sh root applies to a number of things. For example, I sanctify (separate?) the sabbath day (and holidays) through the recitation of the kiddush, a special prayer declaring the nature of the day, said usually over wine. Why wine? I was wondering about that and then I remembered that of all drinks, grape products have the most dietary-law restrictions applied to them! So it would make sense that we celebrate the restrictive nature of the day with a religiously limited product.
There is a euphemism often used in Judaism is the term "kadesha" for a prostitute. The above webpage explains that the term means that the woman has separated herself from community morals but I disagree (respectfully). The term, as I learned it, is a euphemism. A euphemism replaces a positive idea for an inversely negative one so it isn't taken literally. Looking at kadesha and seeing the "separation" sense misses how the word is a euphemism. I see it as saying exactly the opposite of what it means. The woman is a "kadesha" because she is completely UNRESTRICTED in her behavior. So calling her "the restricted one" creates an opposite-based euphemism.
God's name is said to be holy (which could mean that heord "k-d-sh" is a name of God) and in the sense of restriction this makes sense. We are limited as to when and where we can pronounce God's name, and the 4 letter one had incredible limitations -- so much so that when it was uttered people fell on their faces and prayed!
So if the k-d-sh root has to do with restrictions that create or are created by God's commandments then which day is more k-d-sh? Well, certainly there are restrictions on Yom Kippur that do not exist on Shabbat. We are enjoined from 5 categories of behavior, including ones that are integral to our celebration of holidays and the sabbath. Doesn't this make Yom Kippur a more restrictive day and case closed? Not exactly -- because we cannot do these actions (such as eating) we cannot fulfill other religious obligations which would naturally surround them and which would restrict our actions further. We miss some of the restrictiveness of our dietary habits by simply not eating but a day on which we MUST eat becomes more holy because we then have to eat in a particular way. Additionally, there are prayers that we (Ashkenazic Jews) cannot say on Shabbat that we DO say on Yom Kippur. The Avinu Malkeinu is not said on Shabbat but it IS said on Yom Kippur. This would mean that in terms of the kinds of prayers and requests we make, there are fewer restrictions on Yom Kippur, elevating the sabbath in terms of k-d-sh restrictions.
So after all this, what's the upshot? What day is "more" holy, whatever that means? Do we look at the punishment for breaking the restriction and decide that the more stringent the punishment, the more holy the forbidden line that was crossed?
I'll go with "it's a toss up and an unnecessary one." What is the practical implication to calling a day more or less "holy" than another? We are caught up in labels and extremes -- we want the most, the least, the "specialest," but sometimes, these things don't really exist. We need to see that all holy is holy. All limitation is for the sake of heaven and we shouldn't try to create a hierarchy so that we can decide what is more or less important to abide by.