God is unbending in regard to His law. Peter shows this by illustrating that it does not matter who sins or when he sins. Before God ever created man, angels broke the law of God. God, being just and holy, could do only one thing. Because He cannot permit sin to abide in His Kingdom, He had to follow through with the punishment.
John W. Ritenbaugh
The Covenants, Grace, and Law (Part Sixteen)
"Hell" comes from the Greek tartaroo, and it means "a place of restraint." God did not spare the angels, but He cast them down to a place of restraint, a kind of prison.
In Greek mythology, Tartarus was the lowest hell, the place where the Titans (who were defeated by Zeus) were restrained. It is described as being as far below Hades as heaven is high above the earth. As far as we can apply Greek mythology, we can understand that these angels were cast so far down as to be out of sight. Their place of restraint was so far down that one would think they would never be able to crawl out.
God is trying to get across that the angels have been defeated—cast down from heaven to the earth, as Revelation 12 shows. The earth, then, is a place of restraint, a prison, for them.
To add to the imagery, they are bound in "chains of darkness." This amplifies the thought that Peter is making: The demons are restrained. There is some disagreement among scholars whether Peter uses the word that is translated here as "chains" or whether he means "silo." Almost everyone understands what a silo is. To an American, it is a tall, cylindrical object in which grain is stored. To the Greek, a silo was an underground pit where grain was stored. Whether it is a chain or a silo, it does not matter. God is trying to assure us that the demons have been restrained.
They are being restrained because they are facing judgment. Unfortunately for us, they are restrained in the place where we live! The earth is the silo, the storage bin. We are sharing this place with them. Worse, as they would see it, we are intruders in their space. They consider us invaders.
John W. Ritenbaugh
Satan (Part 1)
When God cast them back down to earth, He placed restrictions on their powers and limited them to "their proper domain" or "first estate," that is, the earth. Here, they await their judgment for their rebellion. "Hell" in II Peter 2:4 is tartaroo, a place of restraint for the wicked. Though Satan himself may appear before God's throne in heaven, he and his demons can do only what God allows (Job 1:6-12; 2:1-7).
Richard T. Ritenbaugh
Basic Doctrines: Satan's Origin and Destiny
Regarding “the angels who sinned”, the Bible asserts that “God did not spare” them, meaning that He has not pardoned their sins, just delayed their punishment. The verse goes on to say that, in the meantime, He has “cast them down to hell [tartaroo] and delivered them into chains of darkness, to be reserved for judgment.”
E.W. Bullinger writes that their prison, Tartarus, “is not Sheol or Hades, . . . [but] denotes the bounds or verge of this material world” (A Critical Lexicon and Concordance to the English and Greek New Testament, “hell,” p. 370). Tartarus, then, is a holding place—this material world—where the demons are awaiting their final judgment. Their ultimate penalty is not “chains of darkness” or “everlasting chains under darkness” (Jude 6), but something far more permanent to be rendered in “the judgment of the great day.” This appointed time of judgment still awaits them (see Matthew 8:29).
Paul writes unambiguously that “the wages of sin is death” (Romans 6:23). God also says in Ezekiel 18:4, 20, “The soul who sins shall die.” Scripture does not stipulate that this applies only to humans (soul means “living being”—even God is a soul; see Leviticus 26:11, 30; Isaiah 1:14; Jeremiah 6:8; Zechariah 11:8; Matthew 12:18; Hebrews 10:38; etc.), nor does God's Word ever say that sin can be paid for by a lengthy, even eternal, imprisonment (as many speculate will be the demons' fate). According to these verses, all sin requires death for expiation, and since the Bible does not indicate that demons will repent of their sins and accept Jesus Christ's death to pay for their transgressions, only their own deaths will cover their many terrible sins.
Richard T. Ritenbaugh
Other Forerunner Commentary entries containing 2 Peter 2:4:
1 Peter 3:18-20