It is possible that we have been absolutely certain of something only to find that we were wrong. What we don’t know can be detrimental and devastating. [God] “dealing out retribution to those who do not know God and to those who do not obey the gospel of our Lord Jesus. These will pay the penalty of eternal destruction, away from the presence of the Lord and from the glory of His power” (2 Thess. 1:8-9). Ignorance, in this case, is not bliss. At the beginning of the church in Acts 2, there were things that the audience didn’t know. After the message they couldn’t plead ignorance about the will of God.
It is clear from the text that they didn’t understand what was happening. “And they all continued in amazement and great perplexity, saying to one another, ‘What does this mean?’” (Acts 2:12). Here are some things they didn’t know.
They didn’t know this was the fulfilment of prophecy. Peter begins assuring the listeners that the apostles were not drunk, but that this was the pouring out of God’s spirit (Acts 2:14-19).
They didn’t know they were in sin. The first time we read about “calling on the name of the Lord” is a direct quotation from the prophecy of Joel (Acts 2:21; Joel 2:31). This is tied directly to salvation. We see this again in connection with Paul in his conversion account. “Get up and be baptized, and wash away your sins, calling on His name” (Acts 22:16). Naturally, they would need to understand sin in order to see the need for salvation.
They didn’t know that faith in Jesus as the Son of God, repentance, and baptism lead to salvation. Peter spends some time providing a case for the deity of Jesus from Nazareth (Acts 2:22-36). He starts with “Jesus the Nazarene, a man” talking about the miracles that many of them could have witnessed or at least heard about. He ends with, “Therefore let all the house of Israel know for certain that God has made Him both Lord and Christ—this Jesus whom you crucified” (Acts 2:36).
They didn’t know this was God’s eternal plan. In Peter’s defense of the Christ and the events of that day, he mentions prophecy, acknowledging that was premeditated by God. Also, he mentions that Jesus’ delivery into their hands was “by the predetermined plan and foreknowledge of God” (Acts 2:23). This was supposed to happen.
They didn’t know that they would be added to the eternal kingdom. Those who were obedient were added (2:41). We see again, “the Lord was adding to their number day by day those who were being saved” (2:47). They were added to that eternal plan and salvation that God revealed in their sight.