I am sure you've come across these word pairings before:
- город — град
- смород — смрад
- скользкий — склизкий
- ворота — врата
- ворон — враний
- ворог — враг
- холод — хлад (cf. хладнокровный)
- and so on and so forth
You know you can easily add dozens of examples yourself, off the top of your head.
Now, the way I overheard it somewhere (perhaps in grade school), the град, смрад, вран-, врат- etc. variants all come from Old Church Slavonic, while the город, ворот, ворон etc. are "proper Modern Russian", for lack of a better description. And as I said, there are literally dozens if not hundreds of other examples. There is really an obvious pattern here. And by the looks of it, it's always metathesis at work. And by the looks of it, the Old Church Slavonic variant is almost always the more "formal", "literary", "elevated", poetic one, while the other variants are more colloquial, down-to-earth.
Why would that be? What is the reason behind so many Russian words having been "metathesized" vs. their Old Church Slavonic equivalents, getting that more "elevated" poetic version? Did that happen gradually? Or did the variations sort of develop in parallel over time?
I must say I've never encountered anything quite like this before in any other language I'm remotely familiar with. I'd be most grateful if you could point me to any research on this.