What is the Middle English letter?
“Ye han herd that it was seid to elde men, Thou schalt `do no letcherie.”
King James Bible:
“Ye have heard that it was said by them of old time, Thou shalt not commit adultery”
“Ye han herd that it hath be seid, Iye for iye, and tothe for tothe.”
King James Bible:
“Ye have heard that it hath been said, An eye for an eye, and a tooth for a tooth”
Those are pilcrows or paraphs, a typographical mark that distinguishes paragraphs. The modern version is this (¶); the version in your manuscript is an earlier form (⸿). The shape, reminiscent of the letter C, represents the Latin capitulum, which could be anything from a book chapter to a paragraph-sized chunk of text.
Paraph marks in red or blue (or both) were a common feature of late medieval manuscripts. After a quick search I turned up many results for British Library manuscripts described in such a way. These were the first four:
King’s 321: "Paraph marks in plain red or blue."
Additional 54180: "Paraph marks in alternating red and blue, some with pen-flourishing."
Harley 6580: "Alternating red and blue paraph marks."
Harley 7184: "Paraphs in gold with purple pen-flourishing or in blue with red pen-flourishing."
Paraphs like the ones featured in your sample are common in 14th and 15th century manuscripts. If you scroll to the bottom of the page for Harley 6580, the image will show alternating red and blue paraphs that look similar to those in the Wycliffite Bible. (I’m uncertain of usage rights, so I don’t include it here.)
For this write-up I also consulted the following:
Raymond Clemens and Timothy Graham, Introduction to Manuscript Studies. Cornell University Press, 2007. Figure 2-17 (p. 26) features Newberry Library, MS 23, fol. 42v, which has these same marks, and the paraph is defined on p. 88.
"Pilcrow." Wikipedia, Accessed 8 July 2019. I copied the actual characters ⸿ and ¶ from there.