What is the blood, fire, and vapor of smoke in Acts 2:19-20?
The blood, fire, and vapor of smoke are signs and wonders in heaven and earth that point to the coming tribulation. Peter, quoting Joel, expected these as the next event on the agenda, before the kingdom was established. This is not the current age but the tribulation period.
Les explains that the blood, fire, and vapor of smoke are part of the wonders in heaven and signs in the earth beneath that will occur during the tribulation. Peter, having just quoted Joel, had no inkling that anything else would intervene; he thought the tribulation was the next thing on the agenda. Only later, through Paul, is the current age of grace revealed, as seen in Romans 10, where the same language about calling on the Lord is used but under a different economy—not kingdom ground, but where we are today.