In Acts 10:9-16, while Peter was praying on a rooftop in Joppa, he fell into a trance and saw a vision. He saw heaven opened and something like a large sheet being let down to earth by its four corners. Inside the sheet were all kinds of four-footed animals, reptiles, and birds - creatures that Jewish dietary law classified as unclean. A voice told Peter, "Get up, Peter. Kill and eat."
Peter refused, saying he had never eaten anything impure or unclean. The voice responded: "Do not call anything impure that God has made clean." This exchange happened three times before the sheet was taken back up to heaven.
The vision prepared Peter for the arrival of messengers from Cornelius, a Roman centurion and Gentile. God was teaching Peter that the distinction between "clean" and "unclean" was being set aside under the New Covenant, and that the Gospel was not only for Jews but also for Gentiles. When Peter met Cornelius, he understood the vision's meaning: "God has shown me that I should not call anyone impure or unclean" (Acts 10:28).
The other options refer to different biblical events: a burning bush appeared to Moses (Exodus 3), a ladder to heaven was Jacob's vision at Bethel (Genesis 28), and writing on the wall appeared at Belshazzar's feast (Daniel 5).