The Witches of Endor were a thinly veiled reference to the Witch of Endor consulted by King Saul of Israel just before his defeat and demise...read all about it in 1 Samuel 28 in the Old Testament.
From the beginning of the play the Bard casts MacBeth in the worse possible light.
Remember the first time I read Macbeth and figured Shakespeare knew his Bible at least partially. Now the witches are in congress and the evening news on every single station