The four verses speak of the same thing, and the well-known opprobrious name, the "man of Belial," stands at the head as stigmatizing the man who delights in causing the mischief of which they treat.
Diggeth up evil - i. e., Digs an evil pit for others to fall into. Compare Psalm 7:15.

An ungodly man diggeth up evil - How will the following suit?
Effodiuntur opes irritamenta malorum
"Wealth, the incitement to all evil, is digged up out the earth."
A wicked man labors as much to bring about an evil purpose, as the quarryman does to dig up stones.
In his lips - a burning fire - His words are as inflammable, in producing strife and contention among his neighbors, as fire is in igniting dry stubble.

An ungodly man diggeth up evil: and in his lips [there is] as a (m) burning fire.
(m) For he consumes himself and others.

An ungodly man diggeth up evil,.... Or "a man of Belial" (p), a worthless unprofitable man; a man without a yoke, not obedient to the law of God; such a man digs for sin as for a treasure; nor need he go far for it, he has enough in his own heart, out of the evil treasure of which he brings forth evil things; though he is more solicitious and diligent to search into the sins of others, and dig up them, which have long lain buried; as the Manichees raked up the sins of Austin in his youth; and as the Papists served Beza: but perhaps the evil of mischief is here rather intended, which a wicked man contrives and devises; a ditch he digs for others, though oftentimes he falls into it himself; and so the Septuagint and Arabic versions render it, "digs evils for himself"; not intentionally but eventually; see Psalm 7:15;
and in his lips there is as a burning fire; his tongue is a fire, it is set on fire of hell, and it sets on fire the course of nature; and with its lies, calumnies, and detractions, devours and consumer the good names, characters, and credit of men; and deserves no other than sharp arrows of the Almighty, and coals of juniper; even the everlasting fire and flames of hell, James 3:6.
(p) "vir Belijahal", Montanus, Tigurine version, Mercerus.

Ungodly men bestow more pains to do mischief than would be needful to do good. The whisperer separates friends: what a hateful, but how common a character!

ungodly man--(Compare Proverbs 6:12).
diggeth up evil--labors for it.
in his lips . . . fire--His words are calumniating (James 3:6).

27 A worthless man diggeth evil;
And on his lips is, as it were, scorching fire.
Regarding אישׁ בּליּעל, vid., Proverbs 6:12, and regarding כּרה, to dig round, or to bore out, vid., at Genesis 49:5; Genesis 50:5; here the figure, "to dig for others a pit," Proverbs 26:27, Psalm 7:16, etc.: to dig evil is equivalent to, to seek to prepare such for others. צרבת Kimchi rightly explains as a form similar to קשּׁבת; as a subst. it means, Leviticus 13:23, the mark of fire (the healed mark of a carbuncle), here as an adj. of a fire, although not flaming (אשׁ להבה, Isaiah 4:5, etc.); yet so much the hotter, and scorching everything that comes near to it (from צרב, to be scorched, cogn. שׁרב, to which also שׂרף is perhaps related as a stronger power, like comburere to adurere). The meaning is clear: a worthless man, i.e., a man whose disposition and conduct are the direct contrast of usefulness and piety, uses words which, like an iron glowing hot, scorches and burns; his tongue is φλογιζομένη ὑπὸ τῆς γεέννης (James 3:6).

Diggeth up - Prosecutes his evil designs with great industry. His lips - His tongue is set on fire of hell.