
Normally, words in the Torah look like this. Just the letters - no vowels, no musical notation, nothing. This week's reading is different: there are some DOTS.
But first I'm going to talk about why nothing other than the letters, cos I think it's interesting.
Put on an arch-traditional hat. Now you believe that the Torah was dictated by God, to Moses, on Mount Sinai. God gave Moses the letters; just the letters, nothing else. Later on, the masoretic system of twizzles and oojits (this is a highly technical term) was used in manuscripts so that the Jews would remember how to pronounce the Torah. But we invented those, and it isn't appropriate to add them to God's Torah. A row of letters can have different meanings, depending on how you pronounce it; the different meanings are part of the multi-layered message of the Torah. Vowels remove ambiguity and strip the Torah of meaning. So the Torah, our record of the ultimate divine communication to humankind, stays as it was given.
Now take off that hat and put on a historian's hat. This is making you focus on how the vowel signs weren't invented until a very long time after the alphabet evolved. Probably a lot of people didn't even get to hear about them until decades, or centuries, after they were invented. For a long, long time there would be a cultural awareness that letters basically don't - didn't - have extra marks. Certainly, after a while they are no longer newfangled, and the cultural memory of "vowels didn't used to exist at all" is gone, but add to this a cultural awareness that the sefer Torah is in some way connected to the security of continuity, and you can quite easily see why people might not be inclined to cover the Torah with these newfangled vowel things. It's been replaced by a cultural memory of "this is a text we don't change," with the instinctive corollary "we can't quite explain why, but it makes people feel really weird if we do it, and that's not good for a community."
This, by the way, is an example of how different kinds of Jews can use different language to articulate the same values. Communally, we have a vague kind of instinct that vowels in the Torah aren't good. How we explain that varies, but the practical result is the same; no vowels.

Here's our dotty verse - Genesis 18:9, where some angels disguised as random travellers have arrived at Avraham's tent during siesta time, and he's bounded out to meet them with abundant hospitality. And: ויאמרו אליו איה שרה אשתך ויאמר הנה באהל
Vayomeru elav, ayei Sarah ishtekha? vayomer, hineh baohel - They [the angels] said to him [Avraham], where is Sarah your wife? And he said, see: in the tent. Now, the commentators point out that angels are from God, and therefore they know perfectly well that Sarah is in the tent. Why on earth do they ask Avraham where Sarah is?
Because that's a polite way of starting a conversation, they explain. You know - "Hey, Avraham? How're you? What's up with Sarah?" Okay, that's an acceptable answer.
Now, you can see that three letters of
elav -
to him - aleph, yud, and vav - have dots over them. What does that spell? Ayo. What's the very next word? Ayeh. Ayeh is a word that means "where is she?" Ayo is a word that means "where is he?"
We explain that just like they said "Ayeh," they also said "Ayo." Just like the angels chatted with Avraham and inquired after his wife, they also chatted with Sarah and inquired after her husband.
Which is cute, and a nice extra window into the story. But the rabbis use it to illustrate a point of good manners: when one visits somewhere, they say, one should inquire after the hostess as well as after the host.
Nice for itself, but also awesome for what it's doing with the text. This particular part of the Torah is high on action and low on mitzvot. You can read the text just as an interesting story, and that's nice, but when you mouseover the dots and get the parenthetical storylet, and its associated mitzvahlet of polite behaviour, it stops being just a nice story that you listen to in shul, and turns into an extra thread in the weave that binds Torah, Judaism, and human relationships. This neatly illustrates the idea that the Torah contains more than just the plain text.
If we had vowels, we wouldn't notice the dots. I already suggested that vowels remove ambiguity and take away some of the Torah's layers of meaning. Dots are a hint that there is even more meaning there than we thought, and it would be a pity if we forgot to notice that.