This is the account of the first ever gospel message given after the crucifixion, resurrection and ascension of the Lord Jesus Christ. It describes how the disciples were obeying the command of the risen Lord Jesus to wait at Jerusalem until they received power from on High in the form of the baptism in the Holy Spirit; Acts 1:4 And, being assembled together with them, He commanded them that they should not depart from Jerusalem, but wait for the promise of the Father, which you have heard from me. For John truly baptised with water; but you shall be baptized with the Holy Spirit not many days hence. Acts 1:8 you will receive power, when the Holy Spirit is come upon you: and you shall be witnesses to me both in Jerusalem, and in all Judea, and in Samaria, and to the uttermost part of the earth.
Peter was the disciple to whom Jesus promised in particular; Matthew 16:19 And I will give to you (singular = Peter) the keys of the kingdom of heaven.
For these reasons this particular message of Salvation through the name of Jesus delivered by Peter under the anointing of the Holy Spirit is of unique importance. It was given on the day that the disciples received power to be witnesses of Jesus Christ by the one to whom Jesus gave the keys of the kingdom of heaven!