Shakespeare's audiences would've reacted in many different ways to Macbeth. Some would have enjoyed the sheer spectacle on offer; others would've found the play's dark, supernatural elements particularly interesting. Still others would've enjoyed the play as a fascinating, insightful exploration of the tragic consequences of one man's overweening ambition.

However, there's little doubt that Shakespeare himself would've wanted his audiences to take away with them the important message that any attempt to subvert the existing political order by force invariably leads to chaos and instability.

Only a year before Shakespeare wrote Macbeth, England was rocked by the Gunpowder Plot, an attempt by terrorists to blow up Parliament and wipe out the entire political establishment, including the royal family. The Gunpowder Plotters came frighteningly close to achieving their goal. Had they succeeded, England would almost certainly have been plunged into an extended period of chaos. At the very least, there would've been considerable bloodshed.

In writing Macbeth, Shakespeare wanted to play upon the shock still felt by his fellow Englishmen over the Gunpowder Plot to warn them of what can happen when the natural order of things is disrupted by violence.

In Macbeth, we see the murder of a king and the subsequent establishment of a brutal, murderous tyranny. Whether this is what would've happened had the Gunpowder Plot succeeded we will never know. But Shakespeare, in highlighting the dangers of regicide, wanted to remind his audience that this could've been a distinct possibility had King James been murdered.

Given that we are over 400 years removed from Shakespeare's death, we need to factor in just how much society and culture has evolved and changed within that timeframe. For one thing, it is worth noting that the Early Modern Era was a period of intense religious devotionalism, when Europe was tearing itself apart amid conflicts and wars between Catholics and Protestants.

This intensity of religious fervor must be taken into account. People of this time period tended to believe strongly in the supernatural, and they definitely would have been struck by Macbeth's supernatural themes, particularly by Macbeth's dealings with the witches, in ways modern audiences would likely find difficult to fathom. As other contributors have already pointed out, this was a time period where belief in witchcraft was very real. Let us not overlook that fact.

Additionally, there is the political context of Early Modern Kingship and the degree to which Macbeth, as a betrayer of his liege and a usurper of the throne, represents a corruption of the entire political order. This is actually why the character of Malcolm is so important within the play's structure: Malcolm is the rightful heir to the throne, and proper order can only be restored when the usurper has been defeated, with the legitimate claimant triumphant. These political undertones can be easily missed by a modern audience influenced by modern, secular, democratic values. The same can not be said of an audience from Shakespeare's own day and age.

The final aspect, one which is often missed today but would have been far more apparent in Shakespeare's time, involves the character of Banquo, who was prophesied to father future kings. Banquo was actually believed to be the predecessor to the Stuarts. Thus, these prophesies involving Banquo's descendants are actually in reference to Shakespeare's own royal patron, James I. Viewers in Shakespeare's own day would have been more heavily aware of this connection (to say nothing of James I and his closest supporters).

To answer this question, we need to have a little bit of context about attitudes toward the supernatural during Shakespeare's time.

King James VI of Scotland believed wholeheartedly in the perils of witchcraft, which led to trials against witches that began in 1591 and ended in 1597. Convinced that he was going to be murdered by a coven, he began to study witchcraft and published a volume of these studies entitled Demonology. When he became the King of England in 1603, this obsession continued. Thus, we can conclude that Shakespeare likely included witchcraft in his play to please the king.

Audiences at this time also shared this belief in (and fear of) the supernatural. When the first witch is offended and with her fellow witches casts a spell as retaliation in Act One, Scene Three, Shakespeare's audience would have recognized this as one of the most common charges brought against witches at the time: "mischief following anger." This, as well of the other scenes involving the witches, would have inspired a great deal of fear, anxiety, and fascination in Shakespearean audiences.

As mentioned above, the audiences of Shakespeare's time would have taken the threat of witches very seriously.  The period between the 1400 - 1700 AD in Europe is known as the classical period for witch hunts and witchcraft trials; marked specifically by the trial of Joan of Arc by the English at the beginning of the period, and the hysteria and trials of the Salem witches in 1692 in New England at the end of the period.  Specific laws against witchcraft were passed in England in 1563 during the reign of Elizabeth.  Many people of the time had an almost hysterical fear of witches and would have found the witches in Macbeth quite scary rather than somewhat humerous as they are often considered today.

Since we'll never know for certain how the audiences would have acted seeing the play we have to examine the history and cultural norms surrounding the Elizabethan time period.

Most people during this time period did in fact believe in witches so the audience's reaction to the opening scene and subsequent scenes with the witches were, most likely, taken very seriously. The audience would have reacted more emotionally than audiences do today to the witches on stage. They also would have contemplated what was being said by the witches much more closely. The concept of Evil was a very intellectual topic during this time period. The audience would be frightened and intrigued to see Evil manifested physically on stage by the witches.

How would sixteenth-century audiences react to the witches in Macbeth?

First, we should recognize that Macbeth was not performed until the seventeenth century. Shakespeare composed the work at around the turn of the century. Still, witch hunts were not uncommon at all, especially on the European continent, and there is no doubt that many Europeans still believed in them. England and Scotland (the setting of Macbeth) witnessed a number of witch hunts in the seventeenth century, and of course the Salem trials, which rank among the most famous witch hunts in history, occurred more than eighty years after Macbeth was first performed. So it is important to note that many of Shakespeare's audience would have believed that witches were a reality, not a fantasy conjured up for dramatic purposes. Even some who did not literally believe in witches would have identified with one of the play's central themes: the role played by supernatural forces in the lives of human beings. Sometimes, as the witches in Macbeth demonstrate, these forces could be up to no good. On the other hand, it is worth noting that it is Macbeth himself that takes the actions that lead to his downfall--the witches do not themselves indulge in bloodshed. So Macbeth might have been viewed as a meditation on the interaction between malevolent supernatural forces and the all-too-human characteristics of self-destructive ambition and lust for power.