This use of the phrase “last days” as marking the dawn of the new age of redemption can be seen in Peter’s Pentecost sermon (Acts 2:16–17). Peter demonstrated that the coming of Christ and his resurrection clearly meant that the last days had arrived. “The words ‘in the last days’ (en tais eschatais hērmerais) are a translation of the Hebrew words ‘acharey khen,’ literally, ‘afterwards.’ When Peter quotes these words and applies them to the event which has just occurred, he is saying in effect, ‘We are in the last days now.’”
