There are a number of passages in the NT that state that the Lord is coming soon. I was always confused by them, it has been two thousand years since they were written and Jesus still hasn't come. When I asked preachers about them I was either told that God's concept of time is different from ours (a day is like a thousand years 2Pet 3:8), or that writers made a mistake. I didn't like either explanation. God inspired the bible to be understood, so when he says "soon" he means "soon." If the writers were mistaken about when the second coming was how can we trust anything they wrote. I think there is another explanation: they were referring to a different Day than the Day of Judgement.
To us the destruction of Jerusalem is an interesting historical event, and a wonderful example of prophecy being fulfilled, but we don't spend a lot of time thinking about it. Jesus told his followers that "...at that time there will be great suffering , such as has not been from the beginning of the world until now, no, and never will be" (Mat 24:21). There would be a great falling away, they would he hated by all nations, and false messiahs deceive the elect. I think they thought a lot about that event, the "coming of the Son of Man" (Mat. 24:27). When they wrote that a Day was almost there I think this was the event they had in mind.
What I want to do next is to go though some of the verses that speak of the Lord coming soon and list them with the date that John A.T. Robinson gave them in his book Redating the New Testament. He dates all the books of the NT before the Destruction of Jerusalem. Before we do that I want to list some of the major events that happened before that.
57 AD Paul arrested in Jerusalem
64 AD Rome burns
65 AD Persecution of Christians by Nero, Peter and Paul executed
66 AD Jerusalem rebels
68 AD Nero kills himself
68-69 4 emperors
70 AD Jerusalem destroyed
47-48 James 5:8 "You too, be patient and stand firm, because the Lord's coming is near."
Spring 55 1Cor 7:26-31 "Because of the present crisis, I think that it is good for you to remain as you are...What I mean, brothers, is that the time is short...For this world in its present form is passing away."
Fall 57 Rom 13:11-12 "...our salvation is nearer now than when we first believed. The night is nearly over; the day is almost here."
60-65 1John 2:18 "Children, it is the last hour!"
Spring 65 1Pet 4.17 "For it is time for judgment to begin with the family of God...."
67 Heb 10:25 "...not neglecting to meet together, as is the habit of some, but encouraging one another, and all the more as you see the Day approaching."
Heb 10:37 "For in just a very little while, 'He who is coming will come and will not delay.'"
68-69 Rev 1:3 "Blessed is the one who reads aloud the words of the prophecy, and blessed are those who hear and who keep what is written in it: for the time is near."
Two Roman historians wrote about the persecution of Christians by the Roman government. Suetonius (Nero 16.2) wrote "The Christians, a kind of men given to a new and wicked superstition, were put to death with grievous torments." And Tacitus (Annals 15.44) reported "A vast multitude of Christians were not only put to death, but put to death with insult. They were either clothed in the skins of wild beasts and then exposed in the arena to the attacks of half-famished dogs, or else dipped in tar and put on crosses to be set on fire, and, when the daylight failed, to be burned as lights by night."
The period before the destruction of Jerusalem was at time of intense persecution for Christians. James said that God's judgement would start with them. With that in mind we can understand why Paul, James and John would be continually warning people to prepare themselves.