Magna Carta

I found myself at Euston yesterday, with a spare hour to kill, so I popped into the British Library, like you do, to have a look at the Codex Sinaiticus. A couple of months ago there was the following exchange at St Mary’s LGBT group, which had made me want to go and gaze in awe all over again…

Me: “Well, maybe that phrase in Romans is connected more with the preceding bit, remember there’s no punctuation in the earliest New Testament texts. No capital letters to indicate where sentences begin neither…”
Participants: “What? What?! No-one ever told us that. That can’t be right. It would mean you could never be absolutely certain of what any of the texts mean…”
Me: “Hmmm….”

Anyway, whilst I was there, I got distracted by Magna Carta and particularly by a comment that only three phrases in Magna Carta are still on the statute book in England. One of these guarentees the freedom of the English Church.

Can anyone tell me what that means?

What, in particular does it mean in relation to the Anglican Covenant?