LitCharts assigns a color and icon to each theme in The 5th Wave, which you can use to track the themes throughout the work.
Trust and Belief
Survival and Perseverance
Warfare and Dehumanization
Family
Summary
Analysis
Ben worries that Ringer is an alien, but she says it’s more likely that the eyepieces can’t actually detect the infected—they just detect anyone without a chip. She starts developing a theory about the 5th Wave: that it’s about training a few humans to kill the remaining ones without chips in them. She takes Ben’s hands and says that the two of them are the 5th Wave.
Ringer’s theory about the 5th Wave is similar to what Vosch told Ben, but Vosch slightly twisted the details to make the soldiers of Camp Haven seem like the heroes bringing order. As Ringer reveals, it’s just the opposite, and the cause Ben has been dedicating his life to is actually helping to bring about the end of humanity, not protect it.