He cannot wait for fate to fulfil itself, but anticipates the working out of its decrees by impatiently taking the first step in the other path. The particular illustration of the quality of her resolution which she gives is the strongest she can imagine--the murder of her own babe at a time when to do it would be the utmost conceivable outrage to maternal affection; a deed which she knows she could never do or think of doing, much less swear to do, but which she would do if she had sworn to do it.
To my thinking, it is in perfect keeping with one of the most marked characteristics of Macbeth--his active imagination. She fears his nature, which will not permit him to "catch the nearest way"--that is, to kill Duncan. Perhaps he almost enjoys the intrigue.
The banquet is hours later. I go, and it is done; the bell invites me. Having killed Duncan he returns to Lady Macbeth, full of triumph, but then starts to panic when he realises that it is no small thing to kill a king. Macbeth's career from first to last confirms the estimate we form of him when he hears the predictions of the Witches.
Those words, "We'd jump the life to come," show that, in thinking of the possible consequences in this life--the risk of detection, disgrace, and punishment--he does not for the moment forget or ignore the retributions of another world. In this play a whole scene occurs iii. Nor time nor place Did then adhere, and yet you would make both.