Verse 19
I will show wonders - It is likely that both the prophet and the apostle refer to the calamities that fell upon the Jews at the destruction of Jerusalem, and the fearful signs and portents that preceded those calamities. See the notes on Mat 24:5-7 (note), where these are distinctly related.
Blood, fire, and vapour of smoke - Skirmishes and assassinations over the land, and wasting the country with fire and sword.