Daniel 8 is a "zoom in" of Daniel 7, focusing on two of the kingdoms that rose out of the water like beasts in the former chapter. In this case, we have the Persian empire as the ram, and then we have Greece as the goat, the single horn as Alexander the Great, who utterly destroys the ram, but then he suddenly dies and his kingdom is divided into four. From the horn of Syria, an arrogant, boasting horn comes forth, which is even worse than the little horn in chapter seven. This horn is Antiochus Epiphanus, who attacked and slaughtered the Jews in Jerusalem when he reigned. All of these things are prophesied to Daniel in a vision, interpreted by the angel Gabriel, and yet the history is there to point to some essential truths that we can apply to our Christian walks.
1) When we parallel the time of Antiochus Epiphanus with our own (with recurring periods of history, even) we see that the evil of the world will always seem to get the best of the saints. Just as the Jews were persecuted and over 40,000 of them killed, today we have great persecution of the Christian church, by thought word and deed, by the ungodly. Churches are overrun, the word is not preached, the sacraments are defiled, even today, even by the ungodly who pretend to Christianity. Remember from revelation, the true church is attacked on two fronts, from the unbelieving world, and from within the church by those who profess Christianity but preach falsely. (See the two beasts of Revelation 14)
2) God is in control. We can see this by verse 24: "His power shall be great--but not by his own power." God sets up earthly kings and brings them down again, all for his own glory. This gives us great comfort, because we know that no matter what happens to us on this earthly plane, God has the best prepared for his saints. Also, the nature of prophecy itself is such that it demonstrates that God is in control. Only he knows what is to come, and he reveals it to us, so we can know that he is great. The earthly leaders who conquer have no idea what is to happen next in life, but God does. Belshazzar had no idea that his life was expected of him when the writing appeared on the wall, but God did. Persia had no idea it was going to be defeated by Alexander, but God knew. Alexander didn't know that his life was going to be very short, but God knew.
3) The last verse of the chapter reveals not only how Daniel responds to all of this, but how Christ responds to his role as savior of the world, and how we are to respond as saved children of God.
a) Daniel was overcome and lay sick for some days. The vision, even though it was going to happen to other people in the future (he was going to be dead by then), made him physically ill. Likewise, even though we aren't directly affected by the trials of other Christians in the world, we are to be broken by their plight, as if we were living through it with them. We don't blow the persecutions of others off because they are not happening to us. We pray deeply for their struggles, knowing that they are our brothers and sisters in Christ, and God sees them as closely knit to us. Christ wept over the death of Lazarus, even though he knew that Lazarus would live again. He was grieved at the future fall of Jerusalem, even though he knew that the fate was inevitable, and that the Jews would be responsible for their own demise.
b) Daniel continues about the king's business, despite the horrors of the vision. Jesus says to the Father, "not my will but thy will be done," in the garden of Gethsemane. Both had a job to do, and they persevered through the most debilitating of struggles. So, we, to get through the earthly struggles we undertake, don't try to overpower our surroundings, but we go about the king's business, focusing on the kingdom of God, doing the works he has given us to do, and concentrating on his glory. As a result, we find that our spiritual decays reverse.
c) Although appalled by the vision, Daniel still doesn't understand it. There are many mysteries of the universe that are just unattainable by our minds. Likewise, there are mysteries of God that are withheld from us. Even Christ does not know the hour of his return. That is why we have faith, because it's what we have when we don't understand what is going on. Even when we are to intellectually grasp something, faith must precede understanding, or we will never truly understand. Most of the time, faith is all we have, and when we put our full faith in the Jesus Christ of scripture, no matter what tragedies befall us in our lives, we will be spiritually safe and made eternally alive.
So, we see in Daniel, and of course Christ, qualities that keep us in the kingdom: a contrite heart for others, a dutiful passion for God's work, and a saving, penitent faith in Christ for everlasting life.