This means that the Church as the Body of Christ was an unknown entity. Nothing from the record at Pentecost indicates the Twelve knew anything about the Body of Christ.
Peter and the other disciples knew only about the coming earthly kingdom of God.
"Also I set WATCHMEN over you, saying, 'Listen to the sound of the Trumpet! We MUST be preparing ourselves Spiritually NOW while there is yet some remaining daylight, not trusting in ourselves, the military, or any one, but only in the true and wonderful caring God in heaven above..
So you, son of man: I have made you A WATCHMAN for the house of Israel; therefore you shall hear a word from My mouth and WARN them for Me (Ezekiel 7:6-8; 33:7).
Furthermore, only Paul wrote about the Body of Christ (Romans 12.5; 1 Corinthians 10.16, 17, 12.12, 13, 18, 25, 27; Ephesians 1.23, 2.16, 3.6, 4.4, 12, 16, 5.30; Colossians 1.18, 2.17, 19, 3.15).