How do the witches lull Macbeth into a false sense of security?

The witches in Shakespeare's Macbeth do trick Macbeth into feeling a false sense of security.  They do this in stages. 

First they gain his confidence by making predictions that come true.  In Act I, Scene 3 they refer to Macbeth as "Thane of Glamis," which he is, and as "Thane of Cawdor," which as far as he knows, he is not.  When he is later given the news that the king has made him Thane of Cawdor, he naturally believes that the witches know the future and that he can trust them.  His thoughts then move to the other prediction the witches made:  that he will be king.  Banquo tries to warn him to be cautious:

...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.  (I:3)

Banquo basically sums up the plot of the rest of the play in this speech, but Macbeth continues with his train of thought about becoming king as if Banquo never said a word.  Macbeth is already thinking the unthinkable, that he will need to assassinate Duncan if he is to be king as the witches predict:

...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?...

Second, Macbeth seeks out the witches for more information and assurance.  The second apparition that Macbeth is shown, the bloody child, tells Macbeth that "...none of woman born/shall harm Macbeth" (IV:1).  The third apparition is even more reassuring:

Be lion-mettled, proud, and take no care

Who chafes, who frets, or where conspirers are,

Macbeth shall never vanquished be until

Great Birnam Wood to high Dunsinane Hill

Shall come against him. 

This apparition not only tells Macbeth that he will never be vanquished until a wood moves and comes against him, but describes to him the attitude he should have against those who would plot and fight against him.  Macbeth is reassured and is more confident than ever that what the witches predict will continue to be true and accurate.

Of course, what Banquo predicts sometimes happens does happen.  The invading army camouflages itself with branches as they hide in the wood so Macbeth will not be aware of how many of them there are.  When they move forward to attack Dunsinane, it appears the forest is moving.  The witches have equivocated and fooled Macbeth.  The man not born of woman turns out to be Macduff, whose mother died in childbirth before delivering him.  He was delivered by what we now call a C-section, after his mother had died.  He was born out of a body, the woman was already dead.  Thus, he was not born of woman.

The witches gain Macbeth's confidence and manipulate the situation to trick him into feeling a false sense of security.

Incidentally, equivocation is highlighted by the Porter during a comic relief scene (II:3), adding still another layer to the ideas of illusion and reality.