Carols are poems - of a sort

In early Christian centuries, there weren't any, only plainchant, of which 'O Come, O Come, Emmanuel' is a remnant, though it's most often sung at a faster pace and the long notes are cut short.

Later, the church relaxed its grip a little and allowed adapted folksongs and specially written carols into the canon in the Cs.15-16th - and in churches; 'Personent Hodie,' 'Balulalow' and 'Tomorrow shall be my Dancing Day' show something of the differing traditions. It was around that time that the verses in carols became metred and rhymed, probably because they were easier to fit into a particular and much liked tune and harmony. Carols proper were for dancing, too, or for at least processing around houses, fields and orchards; a few were lullabys, 'The Coventry Carol' being one. Some of them had pagan origins; the Wassail carols and 'The Holly and the Ivy' are examples. 

Not all carols were for Christmas; New Year, Easter, Mayday, Harvest Festival and more Church festivals were celebrated. The Welsh carol 'Nos Falan/Deck the Halls' is a New Year, not a Christmas carol. Then there were carols based on folk legends or extension of scripture; 'As it Fell out on a Bright Summer's Day' is one of those, though it's not very well known except among folk singers.

After the Puritan purges and Cromwell's time and up to the C.19th, new ones were written, often by well-known poets and then contemporary composers. 'In the Bleak Midwinter' and ' Once in Royal David's City' indicate a move away from the 'dancing' Medieval and Tudor carols; they mostly tend to be in slower tempi and no longer have the 'folk' or jolly quality about them. In the main, that tradition extended into the Cs. 20-21st, Britten's 'Ceremony of Carols' being one of the few exceptions.

Personally, I dislike most of the Georgian/Victorian offerings, rhymed though they may be, and prefer the earlier ones. Christmas isn't about singing dirges, but about celebrating new life. Given the time of year, the dark days and the cold, who wants to be reminded of 'The Lyke-Wake Dirge?'

Too, I have a thing against choirmasters, mostly musicologists leading Cathedral choirs, who train them to sing nearly all carols far too slowly - even the originally lively carols. A case in point was this year's Carols at Kings. I know Stephen Cleobury's retiring this year and that he was bound to choose his favourites, but the pace at which he chose to conduct was funereal rather than lively, even for the newly written one or two. I've always thought he's more of a traditionalist than is usually reported, so look forward to the new choirmaster's offering with interest. I hope he may turn out to be a new Barry Rose (of Guildford Cathedral choir fame in the 60s); he knew what he was doing as far as pace goes.

For myself, rhymed, metered and up-tempi 'dancing' carols are what I'd like to see among contemporary works - and choirs.