The juxtaposition of horror and humor in chapter 12 is almost palpable. Also juxtaposed is the true prosperity of God's people versus the pseudo-prosperity of the "worldians".
Horror: Herod kills James with the sword then locks up Peter with intention to snuff him out too (because the Jews were pleased about James's murder). He commands the keepers be executed because Peter disappears. He gets eaten by worms and dies.
Humor: (As Rohan mentioned earlier) The angel has to strike Peter to get him to wake up, and even then, Peter's not sure he's awake. Then he wakes up, but Rhoda leaves him on the doorstep. So he stands out there knocking, knocking, knocking. Those inside tell the girl she's crazy, but she keeps saying it's true, till finally they settle on accepting that it's Peter's angel outside. However, the constant knocking inevitably draws them out, and they see the truth for themselves.
Herod seems to be prospering, what with his riches, capturing Peter, the Jews' approval and that of the Tyre and Sidon citizens. He even is hailed as a god--right before being cut down by the only God.
Things seem a bit dismal for the believers, but they're quick and constant in prayer, and God is pleased to answer. He sends an angel on a recon mission for Peter and eliminates their "big" enemy. Right after that the Bible says, "But the word of God grew and multiplied" (Acts 12:24). Herod's death is insignificant compared to the growth of the gospel.
Today, as we look around, we can recognize that juxtaposition of God's remnant people with those indulging in worldly traditions, the "unseen" war between God and Satan. So often, it seems that God's people are losing the battle, that we're being snuffed out. The world on the other hand is rife with attractive pursuits and material wealth. Who, however, will be asking the rocks to fall on them when Jesus returns (Revelation 6:16)?