Sons of Belial - See the marginal reference note. The phrase is very frequent in the books of Samuel. In the New Testament, Paul contrasts Christ and Belial, as if Belial were the name of an idol or the personification of evil 2-Corinthians 6:15. This probably led to the use of the term "Belial" in the the King James Version, instead of expressing its meaning, which is "mischief, wickedness."

The sons of Eli were sons of Belial - They were perverse, wicked, profligate men; devil's children. They knew not the Lord.
"They know! nor would an angel show Him; They would not know, nor choose to know Him."
These men were the principal cause of all the ungodliness of Israel. Their most execrable conduct, described 1-Samuel 2:13-17, caused the people to abhor the Lord's offering. An impious priesthood is the grand cause of the transgressions and ruin of any nation; witness France, Germany, Spain, Ac., from 1792 to 1814.

Now the sons of Eli [were] sons of Belial; they (k) knew not the LORD.
(k) That is, they neglected his ordinance.

Now the sons of Eli were sons of Belial,.... Not that Eli their father was Belial, a wicked man; but though they had so good a father, they were very wicked men, unprofitable abandoned wretches, that cast off the yoke of the law of God, and gave themselves up to all manner of wickedness:
they knew not the Lord; not that they had no knowledge of God in theory, or were real atheists, but they were so practically; they denied him in works, they had no love to him, nor fear of him, and departed from his ways and worship, as much as if they were entirely ignorant of him; so the Targum,"they did not know to fear before the Lord,''or serve him; or, as Kimchi,"they did not know the way of the Lord,''that is, practically.

THE SIN OF ELl'S SONS. (1-Samuel 2:12-17)
Now the sons of Eli were sons of Belial--not only careless and irreligious, but men loose in their actions, and vicious and scandalous in their habits. Though professionally engaged in sacred duties, they were not only strangers to the power of religion in the heart, but they had thrown off its restraints, and even ran, as is sometimes done in similar cases by the sons of eminent ministers, to the opposite extreme of reckless and open profligacy.

But Eli's sons, Hophni and Phinehas (1-Samuel 2:34), were בליּעל בּני, worthless fellows, and knew not the Lord, sc., as He should be known, i.e., did not fear Him, or trouble themselves about Him (vid., Job 18:21; Hosea 8:2; Hosea 13:4).

Knew not - They did not honour, love, or serve God.