Switch off your TV set ... and listen to some truly strange poetry. Photograph: Corbis

By today, if you're anything like me, you're sick to the back teeth of Christmas cheer and the relentlessly tinselly schedules of the BBC. You've lost count of the number of times you've yelled "humbug!" at the television and you certainly don't find doing so in the slightest bit amusing any more. In short, you're in need of something stern and severe to restore your equilibrium.

Fortunately, I have just the tonic: Resonance FM's broadcast of all the extant fragments of Christopher Smart's Jubilate Agno read by Frank Key and Germander Speedwell.

This programme is something of a first. Or, at least, I'm told that the programme-makers are "almost certain" that the remains of Smart's poem have never been broadcast before in their entirety since they were rediscovered in 1939. Whatever. Starting at midday, I'm hoping that this three-hour epic is going to be one of the highlights of the literary-radio year. Not to mention, very strange.

I'm aware now that I have a duty to describe Jubilate Agno for those readers who don't know what I'm banging on about, but that's easier said than done, because the poem is so damn weird. Something of its nature might be gleaned from Smart's own curious life story. Born in 1722, he possessed a fierce intellect and was made a fellow of Pembroke College Cambridge in 1745 - in spite of the fact that he boozed and whored his way through his undergraduate degree. Just as he was starting to make a name for himself as a poet, and had become friends with leading literary contemporaries such as Samuel Johnson, he was overcome with religious mania. This obsession manifested itself in his habit of accosting pedestrians in St James' Park in London and forcing them to kneel in prayer with him.

The extent of his madness is a matter of debate (at the time Johnson claimed he was quite well and that he would gladly have prayed with him). What is beyond doubt is the fact that Smart was placed in lunatic asylums for large parts of the 1750s and 1760s. It was during his incarcerations that he wrote most of Jubilate Agno.

Put in its simplest and driest terms, this long poem is a hymn of praise to God for all the wonders of the natural world, using the antiphonal patterns of Hebrew poetry, with hundreds and hundreds of phrases beginning with "Let", answered by corresponding verses beginning with "For".

Naturally, since the origins of the poems are so shrouded in mystery, there are all sorts of interesting ideas out there about why it is so very strange. One of my favourite theories (for which I have found no corroborating evidence outside the poem so far, but which is so neat and stated here with such authority that I just want to believe it) is that the content of the poem was heavily influenced by the fact that during his internment Smart had only six books: the King James Bible; Ainsworth's Latin Thesaurus; Salmon's guide for London pharmacists (in Latin); Hill's Useful Family Herbal; Miller's Gardener's Dictionary; and Hill's History of Plants. It might explain some of the more esoteric references - not to mention the frequent praise of Hill himself.

There is considerable uncertainty about how the poem should be read and how much of it should be joined together in call and response manner. But whichever way you read it, the effect is hypnotic. It's probably most famous now for the comical lines about the cat Jeoffrey, who, we are told, "purrs in thankfulness when God tells him he's a good cat" and who "killed the Ichneumon-rat very pernicious by land".

However, something more of the poem's sinewy power, rich cadences and outlandish nature can be gained from odd phrases like the following (extracted almost at random):

Let Shallum with the Frog bless God for the meadows of Canaan, the fleece, the milk and the honey Let Hilkiah praise with the Weasel, which sneaks for his prey in craft, and dwelleth at ambush Let Job bless with the Worm - the life of the Lord is in Humiliation, the Spirit also and the truth. Let Elihu bless with the Tortoise, which is food for praise and thanksgiving.

And:

Let Chelal rejoice with Apios Virginian Liquorice Vetch.

And:

For I shou'd have avail'd myself of waggery, had not malice been multitudinous.

And:

Let Machir rejoice with Convolvulus, from him to the ring of Saturn, which is the girth of Job; to the signet of God - from Job and his daughters BLESSED BE JESUS.

I'd happily list this stuff for far longer, but I'm sure you've got the impression by now - and I hope you'll want to go off and read it, or, indeed, listen to it today. Certainly, when the rest of the broadcasting world is trying to shove costume dramas and nausea-inducing feel good comedies down my throat along with the rest of the Christmas turkey I'm going to be tuning into Resonance FM. And there, thanks to Smart, I will be reminded of what Christmas is really about: 2,000 years of religious insanity and quite a bit of wonderful poetry.