To catch the nearest way.
I believe that this phrase, the 'milk of human kindness,' divorced from its context and become the most familiar of all commonplaces, has done more than anything else towards giving a false twist to the general conception of Macbeth's character. The words kind, kindness are amongst the most difficult words in Shakespeare. The wide original signification of the root, natural, nature, still retained in the noun kind, has been lost in the adjective, which has been narrowed by modern usage to one sort of naturalness, tender-heartedness; though in a derivative form the original sense is still familiar to modern ears in the expression 'the kindly fruits of the earth.' In Elizabethan English, however, the root signification still remained in all usages of kind and its derivatives. In Schmidt's analysis of the adjective, two of its four significations agree with the modern use, the other two are 'keeping to nature, natural,' and 'not degenerate and corrupt, but such as a thing or person ought to be.' Shakespeare delights to play upon the two senses of this family of words: Much Ado, i. i. 26.tears of joy are described as a 'kind overflow of kindness'; the Fool says of Regan that she will use Lear 'kindly,' i.e. according to her nature; Lr. i. v. 15.'the worm will do his kind,' i.e. bite. Ant. and Cleop. v. ii. 264.How far the word can wander from its modern sense is seen in a phrase of the present play, ii. i. 24.'at your kind'st leisure,' where it is simply equivalent to 'convenient.' Still more will the wider signification of the word obtain, when it is associated with the word human; 'humankind' is still an expression for human nature, and the sense of the passage we are considering would be more obvious if the whole phrase were printed as one word, not 'human kindness,' but 'humankind-ness':—that shrinking from what is not natural, which is a marked feature of the practical nature. The other part of the clause, milk of humankind-ness, no doubt suggests absence of hardness: but it equally connotes natural, inherited, traditional feelings, imbibed at the mother's breast. The whole expression of Lady Macbeth, then, I take to attribute to her husband an instinctive tendency to shrink from whatever is in any way unnatural. That this is the true sense further appears, not only from the facts—i. ii. 54.for nothing in the play suggests that Macbeth, 'Bellona's bridegroom,' was distinguished by kindness in the modern sense—but from the context. The form of Lady Macbeth's speech makes the phrase under discussion a summing up of the rest of her analysis, or rather a general text which she proceeds to expand into details. Not one of these details has any connection with tender-heartedness: on the other hand, if put together the details do amount to the sense for which I am contending, that Macbeth's character is a type of commonplace morality, the shallow unthinking and unfeeling man's lifelong hesitation between God and Mammon.
Thou would'st be great;
Art not without ambition, but without
The illness should attend it: what thou would'st highly
That would'st thou holily; would'st not play false,
And yet would'st wrongly win: thou'ldst have, great Glamis,
That which cries 'Thus thou must do, if thou have it,
And that which rather thou dost fear to do
Than wishest should be undone.'