What are the themes taking place in Macbeth Act 1, Scene 3?
Themes don't really take place, they are revealed by the work and inferred by the reader. In Shakespeare's Macbeth, themes/ideas are revealed in bits and pieces, repeated, elaborated on, turned into images and dreams, echoed subtly by character after character. Issues are raised by the actions and words of characters, but they don't smack the reader upside the head and say, "I'm bringing up the idea of equivocation now! Pay attention!" or "I'm mixing up the genders of the characters now, turning females into males. You better notice this!" Themes are developed over the course of the play, they are revealed. So it's understandable that you have trouble noticing them in the third act of the play.
The issue of equivocation that I mention above is one of the themes revealed in Act 1.3. The witches make predictions and one of them soon after proves to be true: Macbeth is named Thane of Cawdor. This in itself is not equivocation (lying, giving only part of the truth, deliberately speaking ambiguously with multiple meanings), so the reader isn't led to suddenly come to a realization that the witches are lying and think: "Oh, the theme of falsehood and lying and equivocation is being introduced here." The reader probably isn't aware of any of this yet. The theme is just being introduced.
Banquo, however, thinks of this possibility. Near the end of the scene he tells Macbeth:
...But 'tis strange;
And oftentimes to win us to our harm,
The instruments of darkness tell us truths,
Win us with honest trifles, to betray's
In deepest consequence.... (124-128)
Banquo is used here to elaborate on the theme that starts with the predictions. He furthers the idea of equivocation that will be a part of the actions and words of the characters throughout the rest of the play.
This is just one theme introduced in Act 1.3. Numerous other themes are revealed: evil, ambition, the unnatural, the grotesque, and others.
Ironically, when Banquo warns Macbeth that the witches may be tricking him in order to later bring him harm, he pretty much summarizes the plot of the rest of the play. But the reader doesn't realize it: the idea is only introduced in his speech, and will be repeated, elaborated on, developed as the play develops.
In the play Macbeth by William Shakespeare, deception is another theme that reveals itself. This is both in terms of deceiving the world, and in terms of self-deception. Macbeth takes in the words of the witches and very quickly learns to internalize them quietly, not disagreeing with them or openly agreeing with them either. It is startling how quickly he is prepared to do this, and very revealing about his character. Within seconds he has taken on board the drift of what they are saying, and taken it to heart and not let on to his friend and colleague his true feelings about the prophecies of the witches. This may well show his propensity for evil - or for psychological illness - early in the play.
One of the most important themes in act 1 scene 3 would be the theme of evil, its temptational nature and its curious double-position both inside and outside man.
The witches might tempt Macbeth but as his first sentence in the scene shows, his mind is already attuned with that of the witches, even before their encounter has happened.
The psychological turmoil, indecision, dilemma are another thematic layer communicated through Macbeth's prompt switches between aside and non-aside.
Themes like vengeance, guilt and even the shipman's insomnia--all these are relevant themes to Macbeth's own tragedy.Then, to add on, there are the themes of trust and its betrayal, the imperial act of violence, supernaturalism itself as other issues.