Final answer:
Abinadi quotes Isaiah 53 in the Book of Mormon to testify of Christ's mission and teach about the atonement.
Step-by-step explanation:
Abinadi quotes Isaiah 53 in the Book of Mormon because it contains prophecies that are relevant to the teachings and story of Jesus Christ. Isaiah 53 is a chapter that describes the suffering of a righteous servant who sacrifices himself for the sins of others. Abinadi uses these verses to testify of Christ's mission and to teach the people about the atonement.