In this chapter, the Philistines defeat Israel, capture the ark of the covenant and slay the two sons of Eli.
This chapter is the beginning of what appears to be another "Judges cycle", where Israel will be again oppressed by their enemies until some heroic figure emerges to rescue them from a self-inflicted national tragedy. I say self-inflicted because the people are sinning against the LORD like how Eli's sons are sinning against the offering. Every one of the Judges cycles began with the people sinning against the LORD, usually through idolatry and worshiping other gods. Since this story is happening at the end of the Judges period, we can imagine it is a similar situation here.
Israel is defeated in battle before the Philistines, and they come up with an interesting solution: to take the ark of the covenant into the midst of their camp, to lead them in battle. Recall how in the desert, the ark of the covenant led the people as they moved from one campsite to another (Num 10:33). In this case, the elders of Israel suggest that bringing the ark will bring about the same kinds of victories they saw against Og and Sihon.
What's interesting is that this is more or less the plot of Indiana Jones and the Raiders of the Lost Ark, which is premised on the talismanic power of the ark of the covenant to guarantee any army invincibility in battle. In fact, there is even a line in the movie when Indiana Jones says that no army with the ark has ever been defeated. Apparently Mr. Jones has not read the book of 1 Samuel, because as we can see in this chapter the army of Israel is routed after they bring out the ark. The point is obvious: the ark of the covenant has no power in itself. It only has power if the LORD gives it power, which is very much in proportion to the righteousness of the people who hold it. That's why it's preposterous to think that the Nazi army (in Indiana Jones's case) could simply take the ark of the covenant and somehow attain its power. It's power is from the LORD, and the LORD cannot be manipulated. In this case it's the same: the LORD will not give power for Israel to defeat their enemies if Israel is worshiping other gods and living contrary to the Law.
One part of this story that I find particularly interesting is how in verse 5 we see the psychological effect of the ark, boosting the morale of Israel and bringing fear into the hearts of the Philistines. If the power of the ark were only psychological, then Israel would have been victorious here as before. However, because God was not with Israel in this battle, the Philistines "take courage" (v. 9) and defeat Israel once again.
What's more, because Israel brought the ark of the covenant into the camp as a weapon of sorts, the ark was captured in their defeat, and the two sinful sons of Eli were killed in the battle. Israel had sought to use the LORD like a tool, bringing victory against their enemies without humbling their hearts before him. As a result, they have neither victory nor the ark that they had thought to use. Eli also dies when he hears about the ark being taken by the Philistines, although he did not stop it from being taken out of the tabernacle.
Lastly, we see that the line of Eli is not completely cut off: Phinehas has a son who is borne soon after his death. The boy is named "Ichabod", which means "no glory", and that must have been an awkward name growing up. He is named after the departure of the glory from Israel, and I can only imagine how that must have affected the people around him. It would be like naming a Japanese boy, "Nuclear" or something. Even just saying his name would be a reminder to the people around him of the hardships their nation has suffered, similar to how Naomi called herself Mara in the book of Ruth. Or perhaps an even closer example is how Rachel, at the moment of her death in Gen 35, named her son Ben-Oni, which means son of my suffering, and it was her husband Jacob who renamed the boy Benjamin.
In this case, it's a name that speaks about more than personal suffering and even more than national suffering. It's a name that speaks of national failure. The departure of glory is not something that happened to them, it was something that they did, that they brought about by their idolatry. Eli and Phinehas's wife die from the grief that came upon them, and that shows the kind of despair the nation is in right now. But we know that Samuel is righteous and "the word of Samuel came to all Israel" (v. 1), so perhaps things will get better, in a time and a way that Israel does not anticipate.