What does Acts 2:23 mean?

Peter is talking to a group of Jews who have traveled from all over the Roman Empire and the Middle East to come to Jerusalem to celebrate Pentecost (Acts 2:9–11). It's unlikely that many of these men were present fifty days prior, during the Passover, when Jesus was crucified. And Peter's words may be directed at the few locals present. But Peter still lays Jesus' death at all their feet.

God's relationship with Israel was unique. To a large extent, it was corporate—God blessed or punished the people for obedience or rebellion that was prevalent across the entire nation. Eternal salvation was individual and required individual faith (Galatians 3:11; Hebrews 11:1–2). But God often held all Jews responsible for what was done under the authority of the leadership, and the crucifixion of Jesus certainly applies (John 19:12–16). Jewish leaders and a Jewish mob delivered Jesus to be crucified by Romans: "lawless men." The ruling council of Jews had no legal reason to execute Jesus under the Mosaic law so they manipulated those outside the Mosaic law to murder Him.

God exists outside of time. When Adam and Eve sinned, He didn't have to spontaneously come up with a plan to save the human race. He always knew Adam and Eve would sin, and He always planned for Jesus to die for us (1 Peter 1:20–21). The first inkling we have is in Genesis 3:15, right after Adam and Eve sinned. But there are many more places in Scripture where God gave His people hints of what would happen (Matthew 26:56; 27:9; Mark 14:49; Luke 22:37; 24:44; John 13:18; 15:25; 17:12; 19:36–37).

"Definite" is from the Greek root word horizō, and "plan" is from the Greek root word boule. "Foreknowledge" is from the Greek root word prognōsis. Together, they mean God understood all possible conditions, outcomes, and variables, and decided His purpose would be best met by the act of Jesus' crucifixion.