The resurrection of Christ is central to Christian faith (1 Cor 15), and part of the radical newness of the gospel. Paul writes that “our Saviour, Jesus Christ, who has destroyed death and has brought life and immortality to light through the gospel” (2 Tim 1:10).
In other words, the afterlife was an opaque or unknown reality in the OT, only brought to light in the NT through the death and resurrection of Jesus Christ. This is the key to the biblical theology of death and resurrection, affirming both the light shed by the gospel and the relative ignorance of earlier times (cf. Mark 9:10).