At the end of both the Apostles’ Creed and Nicene Creed is the profession of belief in “life everlasting.” Full consideration of life everlasting calls to mind the “four last things:” death, judgment, heaven, and hell.
The Catechism of the Catholic Church gives a very tidy summary of the connection these four last things have to one another in paragraph 1022: “Each man receives his eternal retribution in his immortal soul at the very moment of his death, in a particular judgment that refers his life to Christ: either entrance into the blessedness of heaven – after purification or immediately, - or into immediate and everlasting damnation.” Thus, upon our death in this life (when our immortal soul leaves the body), we are immediately judged by Christ as either worthy of life in heaven (even if purification is necessary first) or are consigned to eternal hellfire and separation from God.
The judgment which is referred to in these four last things is the immediate or “particular” judgment that each one receives at the moment of death. In this judgment, each individual receives his or her “retribution,” or their just reward according to their way of living in Christ (or in not living in Him). Throughout the Gospels, Jesus exhorts his followers to remain vigilant as we do not know the timing of death or of his glorious coming. This vigilance is meant to point us toward living constantly in union with Him and the communion of saints – free from sin and reliant upon Jesus Christ through whom our salvation is accomplished. Those who freely give themselves to Christ in faith (through baptism), who humbly seek to live in Him (and yes, this includes good works), and who remain in Him (particularly through the life of the Church and her sacraments) place themselves in greater readiness for this judgment. Those who fall away or reject Christ of their own choosing to be away from him risk the loss of eternal life.
Those judged worthy of heaven receive their reward as life in the unity of the Trinity – dwelling in God’s peace and joy, looking upon Him as He is in what is called the “beatific vision.” While we hopefully live in desire for this reward to be immediate, for many (and probably most) who are judged worthy, an intermediate time of purification is necessary to “purge away” any unholy attachments to this life or to “purify” them of any remaining consequences of sin – and thus they enter the state of purgatory wherein this purification is accomplished. We should never assume that anyone (including ourselves) goes straight to heaven without need of some purification – and therefore we ought to always pray for the deceased in hope of their being judged worthy of heaven – mindful of final purification.
Finally, those who are judged as unfaithful by their own choosing to be such are immediately consigned to eternal hellfire. It is necessary that we acknowledge that hell exists – if for no other reason than that true justice requires it. The reality of hell as eternal separation from God (and thus an unimaginable horror) is not willed by God; it is, however, freely chosen by those who willfully reject God and His mercy (through commission of and remaining in mortal sin) – as the just end of this rejection of God through sin.
These four last things, therefore, are realities that await us. It is therefore important that we always live with awareness of their truth and right vigilance to remain in Christ, free from sin. Likewise it is especially good that we pray for the faithful departed – that they who have been judged worthy might be made perfectly pure and received into heaven.
For further reading: In the Catechism of the Catholic Church, paragraphs 1020 – 1060 give explanation of the four last things, along with the end of the world and the “general judgment” of all the living and the dead.