The plowing - The Hebrew word, with a change in its vowel points, may signify either:
(1) the "fallow field," the "tillage" of Proverbs 13:23, or
(2) the lamp.
According to: (1) the verse would mean, "The outward signs of pride, the proud heart, the broad lands of the wicked, all are evil." (2) however, belongs, as it were, to the language of the time and of the book Proverbs 13:9; Proverbs 24:20. The "lamp of the wicked" is their outwardly bright prosperity.

A high look - The evidence of pride, self-conceit, and vanity. A proud heart, from which the high look, etc., come.
And the ploughing - נר ner, lucerna, the lamp, the prosperity and posterity of the wicked; is sin - it is evil in the seed, and evil in the root evil in the branch, and evil in the fruit. They are full of sin themselves, and what they do is sinful.

An high look, and a proud heart, [and] the (b) plowing of the wicked, [is] sin.
(b) That is, the thing by which he is guided or which he brings forth as the fruit of his work.

An high look, and a proud heart,.... The former is a sign of the latter, and commonly go together, and are both abominable to the Lord; see Psalm 101:5. A man that looks above others, and with disdain upon them, shows that pride reigns in him, and swells his mind with a vain opinion of himself; this may be observed in every self-righteous man; the parable of the Pharisee and publican is a comment upon it; sometimes there may be a proud heart under a disguise of humility; but the pride of the heart is often discovered by the look of the eyes. It may be rendered, "the elevation of the eyes, and the enlargement of the heart" (p); but not to be understood in a good sense, of the lifting up of the eyes in prayer to God, with faith and fear; nor of the enlargement of the heart with solid knowledge and wisdom, such as Solomon had; but in a bad sense, of the lofty looks and haughtiness of man towards his fellow creatures, and of his unbounded desires after filthy lucre or sinful lusts: the Targum renders it,
"the swelling of the heart,''
with pride and vanity;
and the ploughing of the wicked is sin; taken literally; not that it is so in itself; for it is a most useful invention, and exceeding beneficial to mankind, and is to be ascribed to God himself; and of this the Heathens are so sensible, that they have a deity to whom they attribute it, and whom they call Ceres (q), from to plough; it only denotes that all the civil actions of a wicked man, one being put for all, are attended with sin; he sins in all he does. Or, metaphorically, for his schemes, contrivances, and projects, which are the ploughing of his mind; these are all sinful, or tend to that which is so. Some understand this particularly of his high look and proud heart, which are his ploughing and his sin; Ben Melech; and others of his ploughing, or persecuting and oppressing, the poor. The word is sometimes used for a lamp or light, and is so rendered here by some, "the light of the wicked is sin" (r); their outward happiness and prosperity leads them into sin, involves them in guilt, and so brings them to ruin and destruction: and this way go the Targum: Septuagint, Vulgate Latin, Syriac, and Arabic versions.
(p) "elatio oculorum et latitudo cordis", Piscator, Michaelis, Cocceius, Schultens. (q) "Prima Ceres ferro mortales vertere terram instituit", Virgil. Georgic. l. 1. (r) "Incerna impiorum", V. L. Mercerus, Gejerus, Cocceius, Michaelis, Schultens.

Sin is the pride, the ambition, the glory, the joy, and the business of wicked men.

high look--(Compare Margin; Psalm 131:1).
proud heart--or, "heart of breadth," one that is swollen (compare Psalm 101:5).
ploughing--better "lamp," a frequent figure for prosperity (Proverbs 20:20); hence joy or delight.

4 Loftiness of eyes and swelling of heart -
The husbandry of the godless is sin.
If נר, in the sense of light, gives a satisfactory meaning, then one might appeal to 1-Kings 11:36 (cf. 2-Samuel 21:17), where ניר appears to signify lamp, in which meaning it is once (2-Samuel 22:29) written ניר (like חיק); or since ניר = נר (ground-form, nawir, lightening) is as yet certainly established neither in the Hebrews. nor Syr., one might punctuate נר instead of נר, according to which the Greeks, Aram., and Luther, with Jerome, translate. But of the lamp of the godless we read at Proverbs 13:9 and elsewhere, that it goeth out. We must here understand by נר the brilliant prosperity (Bertheau and others) of the wicked, or their "proud spirit flaming and flaring like a bright light" (Zckler), which is contrary to the use of the metaphor as found elsewhere, which does not extend to a prosperous condition. We must then try another meaning for נר; but not that of yoke, for this is not Hebrews., but Aram.-Arab., and the interpretation thence derived by Lagarde: "Haughtiness and pride; but the godless for all that bear their yoke, viz., sin," seeks in vain to hide behind the "for all that" the breaking asunder of the two lines of the verse. In Hebrews. נר means that which lightens (burning) = lamp, נוּר, the shining (that which burns) = fire, and ניר, Proverbs 13:23, from ניר, to plough up (Targ. 1-Samuel 8:12, למנר = לחרשׁ) the fresh land, i.e., the breaking up of the fallow land; according to which the Venet. as Kimchi: νέωμα ἀσεβῶν ἁμαρτία, which as Ewald and Elster explain: "where a disposition of wicked haughtiness, of unbridled pride, prevails, there will also sin be the first-fruit on the field of action; נר, novale, the field turned up for the first time, denotes here the first-fruits of sin." But why just the first-fruits, and not the fruit in general? We are better to abide by the field itself, which is here styled נר, not שׂדה (or as once in Jeremiah 39:10, יגב); because with this word, more even than with שׂדה, is connected the idea of agricultural work, of arable land gained by the digging up or the breaking up of one or more years' fallow ground (cf. Pea ii. 1, ניר, Arab. siḳâḳ, opp. בור, Arab. bûr, Menachoth 85a, שׂדות מניּרות, a fresh broken-up field, Erachin 29b, נר ,, opp. הביר, to let lie fallow), so that נר רשׁעים may mean the cultivation of the fields, and generally the husbandry, i.e., the whole conduct and life of the godless. נר is here ethically metaph., but not like Hosea 10:12; Jeremiah 4:3, where it means a new moral commencement of life; but like חרשׁ, arare, Job 4:8; Hosea 10:13; cf. Proverbs 3:29. רחב is not adj. like Proverbs 28:25, Psalm 101:5, but infin. like חסר, Proverbs 10:21; and accordingly also רוּם is not adj. like חוּם, or past like סוּג, but infin. like Isaiah 10:12. And חטּאת is the pred. of the complex subject, which consists of רוּם עינים, a haughty looking down with the eyes, רחב־לב, breadth of heart, i.e., excess of self-consciousness, and נר רשׁעים taken as an asyndeton summativum: pride of look, and making oneself large of heart, in short, the whole husbandry of the godless, or the whole of the field cultivated by them, with all that grows thereon, is sin.

The plowing - Even their civil or natural actions, which in themselves are lawful, are made sinful as they are managed by ungodly men, without any regard to the glory of God, which ought to be the end of all our actions.