In the gospel according to Mark, there are already hints that the request of the sons of Zebedee to be seated at the right and left hand of Jesus is ironically being connected with the crucifixion narrative, where Jesus is crucified with a brigand on his right and on his left—hence Jesus’ reply, “you don’t know what you’re asking” (Mk. 10:35-45; 15:27).
But this connection is made even more strongly in the gospel according to Matthew, where it is not the sons of Zebedee but their mother who makes the request to Jesus (Matt. 20:20-28). Matthew adds the mother of the sons of Zebedee into the narrative in exactly one other place in his gospel: the crucifixion (27:56). Moreover, these are the only two places in Matthew’s gospel where she appears. Not only that, but the language used to describe the sons’ relationship to Jesus more exactly matches that of the crucifixion narrative. In Mark, the words for the left hand are not the same (granted, they are synonyms: aristeros in the sons’ request and euōnumos in the passion narrative). In Matthew, the phraseology in both texts is identical.
If we assume (as most do) that Mark was written first, it would appear that Matthew has done several things to solidify this connection. In any case, he makes the point still more powerfully. Whereas in Mark, those who make the request do not discover what they were really asking for (since the sons of Zebedee abandon Jesus in the garden), in Matthew the mother of the sons of Zebedee sees with her own eyes what her request would have entailed: the Lord of Glory enthroned “in his kingdom” on the cross, with “one on his right and one on his left.”