@Knight of Serra: I wouldn't say the Azorius are about law for its own sake as about law for the sake of predictability. Hence why a number of them are vulnerable to bribery; they'll take the devil that just revealed its plans over the devil they can't see (e.g. the Orzhov having a plan B if the bribe doesn't go through), if there's no reason to believe there's any third choice. Even beyond bribery and its ilk, the concern for predictability means they're determined to take it (ridiculously) slow and steady; maybe a rapid investigation appals them with the possibility of sloppiness, and resultant chaos, even in quantities of drams? (Next time? Bring murder concerns to the Boros. Preferably the Wojek division.)
@Gruulsmash: While the Babylonian version of the story is the most widely known, it's suspected that each major Mesopotamian place that had the legend used their city's primary god as the one who slew Tiamat and Qingu; the original was probably Enlil or Anu. And yes, after killing her, Marduk/Enlil/whomever used the parts of her body to create the surface world and the skies (i.e. she's the world, or at least her corpse is. Now remember that Mat'Selesnya is called the Worldsoul...). I forget whether Apsu's body was used to create the heavens or the underworld. I do remember that Qingu was used to create humanity, though. I have no idea what, if anything, Mummu's body was used for.
Given that green and white both have a low opinion of black's self-centered tendencies, I'm thinking that my Tiamat'Selesnya hypothesis works best if she's a Well-Intentioned Extremist/Knight Templar, rather than a powerlust-addled character like Oona. Remember that even Bougrat, of the anti-civilization Cult of Yore, thought Ravnica was better off without the (other, at least) Old Gods--they were TOO savage, sadistic, etc. ( Sanguine Praetor
and possibly Excruciator
, anyone?). Mat'Selesnya taking advantage of the city spread to quell the more violent Old Gods, then turning the whole city into the most tranquil wilds possible while still keeping her brethren and their Nephil servants sealed up...best of both worlds. Even if it results in the kind of stagnation Bant, and arguably Naya, suffered. But then, once you achieve (alleged) perfection, change can only be degradation...All for the sake of preserving mortalkind from becoming casualties in Old God squabble-wars.
I don't know whether WotC INTENDED Mat'Selesnya to be a reference to Tiamat, though. As I said, things relating to modern Ravnica are usually derived from Slavic. In other words, I don't know if "mat" has any meaning relevant to Selesnya precepts in any of the Slavic tongues. One might think of "maternal", but that's Latin. I don't know how much linguistic drift there might be between Romantic and Slavic languages.