In Volume 1, Book 1, Chapter 17, Merlin goes to see his teacher, Bleise. Malory does not fully characterize Bleise, who is a figure from older Arthurian lore, but rather alludes to him in a way that helps establish his own authority as a storyteller (in a rhetorical tactic called ethos):
And there [Merlin] told how Arthur and the two kings had sped at the great battle, and how it was ended, and told the names of every king and knight of worship that was there. And so Bleise wrote the battle word by word, as Merlin told him how it began, and by whom, and in likewise how it was ended, and who had the worse. All the battles that were done in Arthur’s days, Merlin did his master Bleise do write; also he did do write all the battles that every worthy knight did of Arthur’s court.
Bleise, or Blaise, appears in many stories about Merlin and Arthur. He is a chronicler, or someone who writes (usually compellingly) about history for the history books. We might think of him today as something between a historian and a journalist, and definitely one who knows how to tell a great story that will stand up generations later. He is also Merlin's teacher in some accounts. Malory suggests that in his version of this world, Bleise holds both of these roles ("master" means, essentially, "teacher").
By alluding to Bleise as a historian of Arthur's court, Malory draws a parallel between himself and Bleise. Malory is writing about the death of King Arthur, but along the way, he too is writing of "all the battles that every worthy knight did of Arthur's court." He is also making claims, both direct and indirect, about the political landscape in his own time, anchoring current events to mystical events from the past that may or may not have happened. The connection Malory draws between himself and Bleise illuminates the book's borderline status between historical document and legend. Within the Arthurian world, Bleise is someone who records historical events. But he is also a legendary figure who appears in different ways in different versions of Arthurian lore. If he is the one who has recorded many of the events in the lore, he seems as motivated to tell a good story as he is to preserve history. In writing about King Arthur's court, Malory is claiming to write a historical text (and pieces of it do have a tenuous basis in history), but he is also consolidating many sometimes-contradictory stories that are more folkloric than historical. Just as Bleise is a part of the legend and also a chronicler of the legend, Malory too sees himself as deeply entangled with both legend and history. Alluding to Bleise helps him establish his own authority as a chronicler of legendary proportions.
In Volume 1, Book 1, Chapter 27, Arthur follows Merlin's advice to have all the children born around May-Day killed because one of them will grow up to destroy Arthur. This incident alludes to two Biblical stories, and it foreshadows Arthur's downfall at the end of the Book:
Merlin told King Arthur that he that should destroy him should be born in May-day, wherefore he sent for them all, upon pain of death; and so there were found many lords’ sons, [...] and all were put in a ship to the sea, and some were four weeks old, and some less.
Arthur's cruelty is startling here. He kills children under four weeks old simply because he thinks one of them will bring about his downfall one day. The story of a king who kills so indiscriminately as an insurance policy would have been familiar to Malory's readers, however. In the New Testament's Gospel of Matthew, when Jesus is born, King Herod of Judea orders all male children under the age of two to be killed so that he will not be dethroned by Christ. This story, called the "Massacre of the Innocents," also resembles a story from the Book of Exodus in the Old Testament. Here, Pharaoh hears that baby Moses will grow up to threaten his power, so he orders all the Israelite children killed. Moses's parents, having foreseen the danger in a dream, conceal Moses so that he survives. Like Moses and Jesus, Mordred too survives Arthur's tyrannical attempt to cling to his power:
And so by fortune the ship drove unto a castle, and was all to-riven, and destroyed the most part, save that Mordred was cast up, and a good man found him, and nourished him till he was fourteen year old, and then he brought him to the court, as it rehearseth afterward, toward the end of the Death of Arthur.
The narrator explicitly states that Mordred's survival works "toward the end of the Death of Arthur." But the biblical allusions strengthen the foreshadowing. With the allusions in mind, Mordred is as destined as Moses or Jesus are in the Bible to become an important figure who upsets the social order. Instead of saving himself, Arthur ironically seals his fate to be dethroned by his own son.
The allusions also capture the book's ambivalence toward Arthur and what he represents. Arthur is committed to certain honorable principles and represents a time for which Malory is somewhat nostalgic. Still, he is also deeply flawed. In this instance, he maps onto the antagonists of the two Bible stories. Mordred will grow up to be bitter and deceitful, but part of the tragedy of "the death of Arthur" is that there is less glory in it than one might expect. Arthur is not just a glorious king toppled by an evil son. In fact, it might be more accurate to say that he is a bad father who gets exactly what he bargained for.
The book contains several allusions to Joseph of Arimathea. For example, in Volume 2, Book 13, Chapter 3, Galahad is introduced as the rightful occupant of the Siege Perilous because he is related to Joseph of Arimathea:
Then the old man said unto Arthur, ‘Sir, I bring here a young knight, the which is of kings’ lineage, and of the kindred of Joseph of Arimathea, whereby the marvels of this court, and of strange realms, shall be fully accomplished.’
In Christian tradition, Joseph of Arimathea is the man who took Jesus down from the cross so that he could be prepared for burial. In some versions of the story (including one of the stories Malory's book relies on), he is related to Jesus by blood. In the French poet Robert de Boron's telling, Joseph of Arimathea kept the Holy Grail safe during a long imprisonment. Jesus had drunk from the Grail at the Last Supper before he was crucified, and this gave it the magical ability to produce endless sustenance for Joseph during his imprisonment. The "Sangreal" is both the Holy Grail (San Greal) and the True Blood (Sang Real) of Christ. For the reader familiar with all these connotations surrounding Joseph, Galahad's introduction as a blood relative of Joseph of Arimathea makes him seem especially suited to hold the Siege Perilous, or the seat of the person who will achieve the Grail.
Allusions usually lean heavily on readers' outside knowledge of a person, event, or literary work and are not explained within the text. Malory does describe his version of Joseph of Arimathea's history in bits and pieces throughout the book. Joseph actually descends from the heavens in Volume 2, Book 17, Chapter 20. Although the explanation and Joseph's literal presence in the book would usually negate the idea that this is really an allusion to Joseph, that is not the case here. Malory's book is tangled up in a huge number of sources for the King Arthur legend, and it allows multiple contradictory versions of events to be true at once. For instance, there are two competing stories within the book about how Arthur came to possess Excalibur. In the passage above, the allusion to Joseph is an effective harbinger of Galahad's significance not just because of what the book has explained about Joseph of Arimathea, but also because of the layered and even conflicting stories about him that Malory's readers bring to the table. For example, readers who know that some of Malory's Joseph of Arimathea material is coming from Robert de Boron's work will recognize that this introduction legitimates not only Galahad's lineage, but also Malory's lineage as an Arthurian storyteller descended from Robert de Boron.