This is an interesting question, because on the one hand you could argue that it is impossible for a modern day audience to relate to an ancient Scottish lord and witches and other such characters. However, I would want to answer this question by the way in which Shakespeare presents this characters, as far distant as they are through time and geography, as being profoundly human, and being subject to the same kinds of desires, hopes and wishes as we have today, which of course makes us able to relate to them and helps us to empathise with them, even if we don't necessarily like them as characters.
Consider the character of Macbeth. What drives him above all is his sense of ambition and his thirst for power. This is of course a massive characteristic that all of us share or have experienced at some point in our lives. Some people are just as consumed by their ambition as Macbeth is. Note the way in which the prophecy of the witches clearly strikes a chord within Macbeth in Act I scene 3:
This supernatural soliciting
Cannot be ill; cannot be good:
If ill, why hath it given me earnest of success,
Commencing in a truth? I am Thane of Cawdor:
If good, why do I yield to that suggestion
Whose horrid image doth unfix my hair,
And make my seated heart knock at my ribs,
Against the use of nature? Present fears
Are less than horrible imaginings.
We can see the beginning of the massive internal conflict that Macbeth faces as he oscillates between thinking the prophecy is a good thing and recognising that it is a bad thing that is being used to tempt him. His struggle about whether to act or not to act on his ambition is one that the majority of the audience can relate to, making him a perfect example of how Shakespeare created characters that could be relevant to an audience.