For four which it cannot bear - Better: four it cannot bear. Here the common element is that of being intolerable, and the four examples are divided equally between the two sexes. Each has its examples of power and prosperity misused because they fall to the lot of those who have no training for them, and are therefore in the wrong place.

For three things the earth is disquieted, and for four which it cannot bear - This is another enigma. Four things insupportable to men. 1. A slave, when he becomes ruler. 2. An overfed fool. 3. An ill-tempered woman, when mistress of a family. And, 4. A servant maid, when the rule of the house is committed to her.
1. A slave, when he comes to bear rule, is an unprincipled tyrant. It has been often observed both in America and in the West Indies, when it was judged necessary to arm some of the most confidential slaves, that no regiments were used so cruelly in the drill, etc., as those black regiments that had black officers.
2. The overfed fool. The intellectually weak man, who has every thing at his command, has generally manners which none can bear; and, if a favourite with his master, he is insupportable to all others.
3. An ill-tempered woman, when she gets embarrassed with domestic cares, is beyond bearing.
4. A servant maid, when, either through the death of the mistress, or the sin of the husband, she is in fact exalted to be head over the family, is so insolent and impudent, as to be hateful to every one, and execrated by all.

For three things the earth is disquieted,.... The inhabitants of it are made very uneasy;
and for four which it cannot bear; they are a load and burden upon it, and are intolerable to those that dwell on it, and make them very uncomfortable.

Four sorts of persons are very troublesome. Men of low origin and base spirit, who, getting authority, become tyrants. Foolish and violent men indulging in excesses. A woman of a contentious spirit and vicious habits. A servant who has obtained undue influence. Let those whom Providence has advanced from low beginnings, carefully watch against that sin which most easily besets them.

Pride and cruelty, the undue exaltation of those unfit to hold power, produce those vices which disquiet society (compare Proverbs 19:10; Proverbs 28:3).

It is now not at all necessary to rack one's brains over the grounds or the reasons of the arrangement of the following proverb (vid., Hitzig). There are, up to this point, two numerical proverbs which begin with שׁתּים, Proverbs 30:7, and שׁתּי, Proverbs 30:15; after the cipher 2 there then, Proverbs 30:18, followed the cipher 3, which is now here continued:
21 Under three things doth the earth tremble,
And under four can it not stand:
22 Under a servant when he becomes king,
And a profligate when he has bread enough;
23 Under an unloved woman when she is married,
And a maid-servant when she becomes heiress to her mistress.
We cannot say here that the 4 falls into 3 + 1; but the four consists of four ones standing beside one another. ארץ is here without pausal change, although the Athnach here, as at Proverbs 30:24, where the modification of sound occurs, divides the verse into two; מארץ, 14b (cf. Psalm 35:2), remains, on the other hand, correctly unchanged. The "earth" stands here, as frequently, instead of the inhabitants of the earth. It trembles when one of the four persons named above comes and gains free space for acting; it feels itself oppressed as by an insufferable burden (an expression similar to Amos 7:10); - the arrangement of society is shattered; an oppressive closeness of the air, as it were, settles over all minds. The first case is already designated, Proverbs 19:10, as improper: under a slave, when he comes to reign (quum rex fit); for suppose that such an one has reached the place of government, not by the murder of the king and by the robbery of the crown, but, as is possible in an elective monarchy, by means of the dominant party of the people, he will, as a rule, seek to indemnify himself in his present highness for his former lowliness, and in the measure of his rule show himself unable to rise above his servile habits, and to pass out of the limited circle of his earlier state. The second case is this: a נבל, one whose mind is perverted and whose conduct is profligate - in short, a low man (vid., Proverbs 17:17) - ישׂבּע־לחם (cf. Metheg-Setzung, 28), i.e., has enough to eat (cf. to the expression Proverbs 28:19; Jeremiah 44:17); for this undeserved living without care and without want makes him only so much the more arrogant, and troublesome, and dangerous. The שׂנוּאה, in the second case, is not thought of as a spouse, and that, as in supposed polygamy, Genesis 29:31; Deuteronomy 21:15-17, as fallen into disfavour, but who again comes to favour and honour (Dathe, Rosenmller); for she can be שׂנואה without her own fault, and as such she is yet no גּרוּשׁה; and it is not to be perceived why the re-assumption of such an one should shatter social order. Rightly Hitzig, and, after his example, Zckler: an unmarried lady, an old spinster, is meant, whom no one desired because she had nothing attractive, and was only repulsive (cf. Grimm, under Sir. 7:26b). If such an one, as כּי תבעל says, at length, however, finds her husband and enters into the married relation, then she carries her head so much the higher; for she gives vent to ill-humour, strengthened by long restraint, against her subordinates; then she richly requites her earlier and happily married companions for their depreciation of her, among whom she had to suffer, as able to find no one who would love her. In the last case it is asked whether כּי־תירשׁ is meant of inheriting as an heiress (Aquila, Symmachus, Theodotion, the Targ., Jerome, the Venet., and Luther), or supplanting (Euchel, Gesenius, Hitzig), i.e., an entering into the inheritance of the dead, or an entering into the place of a living mistress. Since ירשׁ, with the accus. of the person, Genesis 15:3-4, signifies to be the heir of one, and only with the accus. of peoples and lands signifies, "to take into possession (to seize) by supplanting," the former is to be preferred; the lxx (Syr.), ὅταν ἐκβάλῃ, appear to have read כּי־תגרשׁ. This גּרשׁ would certainly be, after Genesis 21:10, a piece of the world turned upside down; but also the entering, as heiress, into the inheritance, makes the maid-servant the reverse of that which she was before, and brings with it the danger that the heiress, notwithstanding her want of culture and dignity, demean herself also as heiress of the rank. Although the old Israelitish law knew only intestate succession to an inheritance, yet there also the case might arise, that where there were no natural or legal heirs, the bequest of a wife of rank passed over to her servants and nurses.

Four - Which are intolerable in human societies.