Maelgwn duly does make an oath now, though it's framed in the Christian telling as promises of atonement for being naughty.
He commits to giving land and funding for Tydecho's Church, though that's suspect, given that Mawddwy wasn't in Gwynedd in the 6th century and therefore not Maelgwn's territory to donate. It may be an element added later to provide more weight to his contrition, or to add a date of 520 CE to the telling.
The Gwynedd ruler furthermore swears to uphold 'the privilege of sanctuary for a hundred ages so that neither man nor beast could be taken from his land; no battles, or burning, or killing to be admitted there.'
In other words, a sacred place where everything runs wild and free. No social constraints. Peace.
Could this be why the legends also tell us that Maelgwn didn't fight at Camlan? He arrived with an army, which Arthur expected to help him win the day. But instead Maelgwn remained stationed in Brithdir, just across the valley, possibly condemning Arthur by inaction.
Finally Tydecho allows Maelgwn to rise from the blue stone Gorsedd. Every bard, however enlightened, has to enter the world again. Unmentioned, but a logical progression, is Tydecho's final role in the shamanic journey.
The gatekeeper - the House of Twilight - has two dwellings. Himself, and the place at the foot of the mountain. This is the final location for an initiate, a resting place for quiet contemplation, or a halfway house between the Otherworldly realm and reality.
That this is marked by a standing stone, within a grove of ancient yew trees, enclosed by the churchyard walls of St Tydecho's Church, shows just how long this has been a sacred site. Three religious eras encased around each other, like layers in the same, old story.
Representing the focal point for a Christian tale, embedded with Druidic symbolism, incorporating ancient monuments which were built to serve an older religion yet.
As for Tydecho and Tegfedd, they might be Christian saints terribly slandered by fertile imagination. But if not, then might they be more than a God and Goddess of the Druids, reconstructed through history and inspired visions?
Could they even represent some distant memory of ancestral deities? Filtered through two religions from another, that we couldn't even begin to reconstruct. Perhaps one where the Wild Hunt held real and present danger, and the fair graves were filled, but the promised reward was worth lugging a heavy blue stone, all the way from Caer Angli, to a spot halfway up a mountain in Mawddwy.