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I was recently rereading the play, which is unfortunately a text for our times, and noticed a few interesting things:

1. Duncan in 1.5:

DUNCAN
Welcome hither:
I have begun to plant thee, and will labour
To make thee full of growing

There's an invisible pun on "labour" here, I think, that quietly works with "full of growing," and also serves as a bridge between the play's repeated language around work ("double, double, toil and trouble") and children. These two themes both appear in surrounding lines:
MACBETH
The service and the loyalty I owe,
In doing it, pays itself. Your highness' part
Is to receive our duties; and our duties
Are to your throne and state children and servants,
Which do but what they should, by doing every thing
Safe toward your love and honour.

DUNCAN
Welcome hither:I have begun to plant thee, and will labour
To make thee full of growing. Noble Banquo,
That hast no less deserved, nor must be known
No less to have done so, let me enfold thee
And hold thee to my heart.

BANQUO
There if I grow,
The harvest is your own.

DUNCAN
My plenteous joys,
Wanton in fulness, seek to hide themselves
In drops of sorrow. Sons, kinsmen, thanes,
And you whose places are the nearest, know
We will establish our estate upon
Our eldest, Malcolm, whom we name hereafter
The Prince of Cumberland; which honour must
Not unaccompanied invest him only,
But signs of nobleness, like stars, shall shine
On all deservers. From hence to Inverness,
And bind us further to you.

MACBETH
The rest is labour, which is not used for you:
I'll be myself the harbinger and make joyful
The hearing of my wife with your approach;
So humbly take my leave.

2. I think there's an artful contradiction between the initial description of Macbeth's brutality at 1.2, which introduces his character, and Lady Macbeth's later concern that he is "too full o' the milk of human kindness" to conduct the murder of Duncan*. I think that we accept her concern in that moment because the Macbeth that we actually meet in Act 1 is thoughtful, and only reverts to the type of cruelty that his initial description would suggest after the murder, at which point an audience has already long forgotten its prior agreement with Lady Macbeth's description.

* She says "too full o' the milk of human kindness / to catch the nearest way," which has to be a quiet pun on "way"/"whey".

3. Isn't it a little strange that Macbeth sees the ghost of Banquo (at a banquet, naturally), whose murder he is responsible for but does not commit himself, rather than a ghost of Duncan, whose  murder he does? Shouldn't Macbeth have significantly more guilt about the latter? Wouldn't context lead us to expect a ghost of Duncan?

4. I think that a ongoing concern in Shakespeare's language is the use of words that are exactly right and exactly wrong at the same time: "Death...from whose bourn...," as Stephen Booth points out in "On the Value of Hamlet." In that context, I've become slightly obsessed with "success" in Macbeth's speech about whether "the assassination / could trammel up the consequence / and catch with his surcease success" in 1.7. "Success" meaning "completion" or "accomplishment" of the murder and the kingship, but also introducing an idea of "succession," exactly the wrong thing for Macbeth to be thinking about when he is ruminating on his reward for killing Duncan, per the witches' prophecy.