Banquo is the ultimate symbol of goodness. Proof of this is his refusal to be tempted by Macbeth in Act 2, sc i. His reaction to the witches' prophecy shows his wisdom, as he is cautious and knows not to rely on the witches' word.
Unlike Duncan (the other symbol of ultimate goodness), he is shrewd and wise; he knows that openly voicing his misgivings against Macbeth and particularly his suspicious ascension to throne after Duncan's death would not be prudent. He is instead cautious and never reveals his innermost thoughts concerning this matter.
Although Banquo is as courageous as Macbeth on the battlefield, he is often overshadowed by his colleague, as can be seen by Duncan's extravagant praise for Macbeth's bravery against the invaders, and his brief address to Banquo as an afterthought. Yet Banquo does not show any envy. His reaction when Macbeth becomes Thane of Cawdor shows that he is not in the least envious. His speech in response to Duncan's praise is also short, respectful, and sincere; in his straightforward way, he even makes a little joke.
Being morally upright himself, Banquo does not even consider that he may become victim to Macbeth's evil ambition, especially as Macbeth feels that "his genius is rebuked" by Banquo." Unlike Macduff, who escapes to England, Banquo remains behind, and suffers the consequences: he is murdered at Macbeth's command, by the Three Murderers while he is out horse riding with his son, Fleance.
Shakespeare uses the character of Banquo to emphasize the wrong path taken by Macbeth. It is Banquo's children, not Macbeth's, who will inherit the Scottish throne, if the witches are to be believed. Like Macbeth, Banquo tends to think ambitious thoughts, as he himself admits in Act II, scene I, that he is losing sleep over "these cursed thoughts." However Banquo does not translate his "cursed thoughts" into action, and prefers to leave things up to fate and God. At the end of the play, although Fleance does not inherit the throne as yet, it is likely that he will do so in the future. It makes sense, then, that Banquo came back after his death to haunt Macbeth. He stands as a rebuke to Macbeth, symbolizing the path he chose not to take: the path where prophecies and heart-felt desires may be fulfilled without evil deeds and clever crimes.
