I will try to give you a brief background to the books in the Bible within which this type of literature is situated. I will not go into any interpretation because it would require a much more extensive response than my allotted space allows. If you are interested in further explanation, I suggest you attend some of Archbishop Thomas Collins' teachings on the topic in his Lectio Divina or other talks.
The Torah, the Law
The first five books in the Bible, the Torah or the Law, give us stories of creation, the early Hebrews and the Exodus, as well as regulations for the Hebrews to observe to remain faithful to their covenant with God. The historical books tell about leaders of the people such as Judges and Kings.
The prophets preach return to God for the people unfaithful to God's covenant, in addition to assuring them that God is always there for them. The writings include Psalms, Job, Proverbs, which are philosophical, poetic and/or historical texts. Within this classification are books like Daniel which form an important part of apocalyptic literature.
In the New Testament, we have the four Gospels and the epistles followed by Revelation, sometimes called Apocalypse. In the Jewish world, apocalyptic writings (not all of which are included in the Bible) were common during the two centuries before and after Christ.
The theme of apocalyptic literature is the end-times, the last stage of humanity and the world, as well as the arrival of the kingdom of God. Towards the end of the church year and during Advent, we use these readings to connect the end of the church year with the end of time. Remember, during Advent, besides preparing to celebrate Jesus' birth into our world 2,000 years ago, we remind ourselves of Christ's Second Coming at the end of time.
As, in a sense, both foretell the future, I'd like to compare the apocalyptics to the prophets. The prophets received the word of God directly and they spoke it to the people bluntly and clearly. The apocalyptics' knowledge usually came in mysterious symbolic visions which required explanation by angels.
The prophets were concerned with Israel and David's royal family from whom the Messiah was to come. However, apocalyptics instead focused on a cosmic mission. Both groups based their faith on God's intervention in history. However, apocalyptic writers, since they were interested in God's world-wide rule, did not detail Israel's liberation by God like the prophets did.
The prophets concentrated on the about-to-happen reward from God for those who repented. Apocalyptics asserted that God would transform the world at the end to bring about the kingdom. Realizing that the permanence of the Jewish nation was in danger due to persecution and domination by other nations, the apocalyptics wrote to strengthen the faith of their suffering contemporaries stressing God's triumph in the end.
Keep your lamps lit
Therefore, even though these writings are difficult, they can serve for us, too, as an assurance that, in spite of any suffering we may have to endure, ultimately God's reign will come about. But Jesus warns us to keep our lamps lit, to be ready for we won't know when the end will come: "Keep awake, therefore, for you know neither the day nor the hour" (Matthew 25:13).
The Gospel of Mark is stronger in its expression: "But about that day or hour, no one knows neither the angels in heaven, nor the Son, but only the Father. Beware, keep alert for you do not know when the time will come" (13:32-33).