In Shakespeare's day, Europe was engulfed in a witch craze that spanned many years of the 16th century, primarily in France, Germany and the British Isles, and it eventually found its way to the North American Colonies in the latter half of the 17th century (specifically the Salem Witch Trials of 1692-3).
A book penned in 1486 by two Germans (Kramer and Sprenger) functioned as a sort of manual for witch-hunters (or witch finders as they were also called): The Hammer of Witches or Malleus Maleficarum. The book gave many tell-tale signs for identifying witches, tips for extracting confessions, and other practical advice, but was also a misogynistic diatribe that included statements such as "All witchcraft stems from carnal desire, which in women is insatiable." The sexual nature of witches was well known in Shakespeare's day, and this sexual undercurrent can be seen in the way that Lady Macbeth manipulates her husband to plan his rival's murder.
In Elizabethan times, people were very superstitious. They believed in the power of witches and feared them. People believed that they could affect the weather, put curses on people, and have all kinds of supernatural powers to create evil. In fact, Macbeth’s audience feared even the witches in the play because of these beliefs. Apparently, Shakespeare included real chants from witches of the day. You could imagine the reaction to this.
On the other hand, people during Shakespeare's era did not enjoy the idea that their lives were subject to fate or destiny. They wanted to believe in free will, in the idea that they made legitimate choices that significantly affected the path and outcome of their lives. This preference also helps to shape drama of the 1600s as opposed to ancient Greek drama, where fate and the gods were very much in control, despite what humans might do to try to thwart it and them.
Therefore, a tension exists in Macbeth: do the witches really know the future (meaning that the future is fated and objectively knowable) or are they lying, manipulating Macbeth by claiming to know the future, in order to see if they can corrupt him? After all, they do discuss the idea that they will make good things seem bad and bad things seem good: "Fair is foul and foul is fair. / Hover through the fog and filthy air." This is manipulative; if they really knew the future, why would they need to dissemble?
Moreover, when they tell him that he'll become Thane of Cawdor, he doesn't know that this has already happened, that they aren't actually predicting the future. Then, when Macbeth learns that he is, in fact, the new Cawdor, it seems to him that the witches do know the future (when they really have just told him a fact of which he was not aware). Thus, there is proof to suggest that, though the sisters may have some supernatural abilities, they do not actually know Macbeth's destiny, that they only tell him they do in order to manipulate him.