Greek for ‘presence’, and used in the NT for the coming of Christ within an eschatological complex including judgement and resurrection—though the word can also denote simply the ‘presence’ of an apostle among his flock (2 Cor. 10: 10).
The parousia of Christ must be understood against a Jewish background of the national hope of a future vindication. It is expressed in Dan. 7: 13 in terms of a Son of Man (meaning Israel) triumphing over beasts (meaning the Gentile nations). The Christians took over Jewish apocalyptic imagery and transformed the eschatological dimension in that the main elements of the coming of the kingdom of God had already been realized in the life of Jesus and in his death, which had been vindicated by the resurrection (1 Cor. 15: 23–4). But the Temple still stood in Jerusalem although Jesus had foretold its destruction (Mark 13: 2). As long as it survived, the heart of the Jewish system was being perpetuated. When it was destroyed by the Romans in 70 CE, Christians could claim that its place was taken by the crucified and risen Son of Man, the new focus of divine presence.
The hope which Paul expected of a coming day of the Lord was not for the end of the world and of time (2 Thess. 2: 2) but for the judgement on mankind (1 Cor. 4: 5) and the final conquest of evil (1 Cor. 15: 24–5). Then the resurrection of Jesus would be consummated by the resurrection of all the faithful and a renewed creation—a kingdom of peace, justice, and love (Rom. 14: 17). Thus Paul and his contemporaries awaited the destruction of the Temple; after 70 CE this historical event of apocalyptic significance became a further vindication of Jesus' message. The fulfilment of what he had predicted for the near future guaranteed the fulfilment at the ultimate. And what still remained to come in the future was the End, when Christ would hand over the kingdom to God the Father (1 Cor. 15: 24). It would constitute the parousia. It could happen suddenly (1 Thess. 5: 2) but, apart from 2 Pet. 3: 3–4, there was no reported dismay or despondency about any delay. Certainly the return of Christ at some time was hoped for, and by some groups has been in the past, and still is, awaited at a precise date in the near future, but that was not the mainstream Christian conviction. The return of Jesus (Acts 1: 10 ff.) is regarded as part of the ultimate future when the whole created order will be renewed; then evil will be judged and defeated; and in such a scenario there would have to be a place for Jesus. But for the early Church the most important part of the process had already occurred with Jesus' resurrection. The timing of the remainder was unimportant.