What does Acts 3:17 mean?

Peter's concept of guilt may sound harsh. He is speaking to a crowd of Jews in Solomon's Portico, across from the temple. It's likely many of them are residents of Jerusalem and were present at the Passover when Jesus was crucified. It doesn't follow that they were all part of the crowd who demanded Jesus be crucified and Barabbas be released (Matthew 27:20–23). But God interacted with the Jews collectively: if they obeyed Him as a whole, He blessed them as a whole; if they rebelled against Him as a whole, He punished them as a whole (Deuteronomy 28:1–6, 15–19). Their corporate identity resulted in corporate culpability. That is why Daniel, a righteous God-follower, could confess the sins of the Jews as if they were his own (Daniel 9:1–19).

Now, Peter explains that they are guilty of Jesus' murder even though they acted in ignorance. Granted, "ignorance" is a relative term. The people of Israel—and especially their religious leaders—had the Jewish Scriptures that prophesied the description of the Messiah (Isaiah 7:14; 9:6; Zechariah 9:9). But because they did not have a strong relationship with God, they could not recognize that Jesus was their Savior (John 15:21). Later, Paul will explain that the prophecies about Jesus' death (Psalm 22:16–18; Isaiah 50:6; 53:3–7; Zechariah 12:10) were fulfilled because the perpetrators didn't understand the prophecies: "For those who live in Jerusalem and their rulers, because they did not recognize him nor understand the utterances of the prophets, which are read every Sabbath, fulfilled them by condemning him" (Acts 13:27).

We sometimes try to bargain our way out of guilt for our sins. We claim we didn't know; or we didn't have a choice; or although we were part of a group that espoused those beliefs, we weren't present at that particular time when the beliefs were manifested as harm to another. The Bible is clear: we are born sinful (Psalm 51:5). Certainly, there are mitigating circumstances, and accidents do happen. But if our leg is broken, it doesn't matter whether it was entirely our fault, or entirely someone else's fault—we go to the doctor and get it taken care of. So, when we sin, we need to deal with it. We must repent, accept Jesus' forgiveness, and ask Him to work in our heart so we grow in righteousness.

We should also be grateful that His death gave us these options. Pride and defensiveness just get in the way. Jesus says, "Blessed are the poor in spirit, for theirs is the kingdom of heaven" (Matthew 5:3). Those who willingly acknowledge their spiritual bankruptcy before God will be welcomed into the world where His grace and love reign. That's an overwhelming reward for just being honest with ourselves.