Judgment on Abominations
Because of the people's refusal to obey, God has Jeremiah tell them to cut off their hair—an apparently figurative reference. "The Heb[rew] feminine form tells us that it's Jerusalem [rather than Jeremiah] who is to cut her hair. The reference is to a person who made a Nazarite vow and was set aside as holy [as all Israel was supposed to be in a sense]. If defiled, one had to cut off his or her hair to symbolize pollution [see Numbers 6:1-21]" (Bible Reader's Companion, note on Jeremiah 7:29).
The Jews had gone so far as to set up abominations—idols and pagan altars—in the temple of God (this having occurred a few decades earlier during the reign of Manasseh). And they went further still, sacrificing their children at Tophet: "In the valley of Hinnom, a gruesome place throughout the history of Judah, King Manasseh had built an altar to the pagan god, Molech. There the children of worshippers were burned on a fiery altar as sacrifices to the pagan god. 'Topheth' means 'fireplace' or 'furnace' and was probably the name of a pit dug in the ground for this abominable ritual" (Russell Dilday, Mastering the Old Testament, 1987, Vol. 9, p. 484).
Of this ghastly practice, God says, "...which I did not command, nor did it [even] come into My heart" (Jeremiah 7:31)—seeming to imply that they believed God had commanded it. Why would they have thought such a thing? Because their worship was syncretistic—blending paganism into the true religion. The Hebrew word for "Lord" was Baal, a name that also denoted the false sun god. And God was their King, the Hebrew word for which was Melek or Molech, another name denoting a pagan deity. Many thus believed that the Lord and King—in their mind the true God—had commanded their traditional religious practices, when these practices had actually come from paganism. God would not accept such worship even if people believed they were properly serving Him through it (see Deuteronomy 12:29-32).
God says the Valley of Hinnom (Gai Hinnom or, in the Greek New Testament, Gehenna) will be renamed the Valley of Slaughter—"so named because of the great slaughter of the Jews about to take place at Jerusalem: a just retribution of their sin in slaying their children to Moloch in Tophet" (Jamieson, Fausset & Brown's Commentary, note on Jeremiah 7:32). However, it is likely that this is also representative of the terrible punishment to come on Judah and Israel in the end time. It may also be typical of the final judgment on all rebellion since the New Testament 12 times uses Gehenna as a designation for the place of final punishment, where the incorrigibly wicked will be burned up—called the "lake of fire" in the book of Revelation.
In chapter 8, we see the propensity of conquering nations to dishonor the dead. In ancient times, they would often dig up the graves—usually tombs and ossuaries—for anything of value to plunder (verses 1-2). This was, of course, looked upon as a horrible desecration. The point is that death and destruction are not the full measure of punishment. The people are also to suffer national ignominy and shame. The ones who aren't dead will wish they were dead—being dragged away as slaves (verse 3).
God laments that His people are perpetual backsliders (verse 5). He heard their past cries for relief and rescued them many times—but they just won't turn their lives around (verse 6). In verse 7 God points out that while birds know when it is time to take major action in migrating, responding to promptings God has put within them, human beings seem oblivious to God's promptings to obey Him—the increasing calamities intended as warnings.
In verses 8-9, the educated people who are supposed to be preserving and teaching God's Word have actually rejected it—and proclaim falsehood instead. As the apostle Paul later remarked of pagan philosophers, "Professing to be wise, they became fools" (Romans 1:22).
Warning of judgment then, God repeats the reason He gave for it in Jeremiah 6:10-15 (8:10-12). God tells Jeremiah that punishment is coming (verse 13), whereupon the prophet relates the sentiments the people will express when judgment falls (verses 14-16). Forces of enemy invasion are described in the past tense to demonstrate the certainty of their coming—and, terrifyingly, they are declared to be God's forces (verse 16)—carrying out His will—and likened to the plague of serpents He sent among the ancient Israelites when they rebelled in the wilderness (verse 17; see Numbers 21:6).