A: Here are several quotes from the UB that speak to your question ...
On several occasions Jesus had made statements which led his hearers to infer that, while he intended presently to leave this world, he would most certainly return to consummate the work of the heavenly kingdom. As the conviction grew on his followers that he was going to leave them, and after he had departed from this world, it was only natural for all believers to lay fast hold upon these promises to return. The doctrine of the second coming of Christ thus became early incorporated into the teachings of the Christians, and almost every subsequent generation of disciples has devoutly believed this truth and has confidently looked forward to his sometime coming.
If they were to part with their Master and Teacher, how much more did these first disciples and the apostles grasp at this promise to return, and they lost no time in associating the predicted destruction of Jerusalem with this promised second coming. And they continued thus to interpret his words notwithstanding that, throughout this evening of instruction on Mount Olivet, the Master took particular pains to prevent just such a mistake. (176:2.2)
Of all the discourses which the Master gave his apostles, none ever became so confused in their minds as this one, given this Tuesday evening on the Mount of Olives, regarding the twofold subject of the destruction of Jerusalem and his own second coming. There was, therefore, little agreement between the subsequent written accounts based on the memories of what the Master said on this extraordinary occasion. Consequently, when the records were left blank concerning much that was said that Tuesday evening, there grew up many traditions; and very early in the second century a Jewish apocalyptic about the Messiah written by one Selta, who was attached to the court of the Emperor Caligula, was bodily copied into the Matthew Gospel and subsequently added (in part) to the Mark and Luke records. It was in these writings of Selta that the parable of the ten virgins appeared. No part of the gospel record ever suffered such confusing misconstruction as this evening's teaching. But the Apostle John never became thus confused. (176:2.8)
Jesus did, on numerous occasions and to many individuals, declare his intention of returning to this world. As his followers awakened to the fact that their Master was not going to function as a temporal deliverer, and as they listened to his predictions of the overthrow of Jerusalem and the downfall of the Jewish nation, they most naturally began to associate his promised return with these catastrophic events. But when the Roman armiesv leveled the walls of Jerusalem, destroyed the temple, and dispersed the Judean Jews, and still the Master did not reveal himself in power and glory, his followers began the formulation of that belief which eventually associated the second coming of Christ with the end of the age, even with the end of the world. (176:4.2)
When Jesus' immediate followers recognized their partial failure to realize his ideal of the establishment of the kingdom in the hearts of men by the spirit's domination and guidance of the individual believer, they set about to save his teaching from being wholly lost by substituting for the Master's ideal of the kingdom the gradual creation of a visible social organization, the Christian church. And when they had accomplished this program of substitution, in order to maintain consistency and to provide for the recognition of the Master's teaching regarding the fact of the kingdom, they proceeded to set the kingdom off into the future. The church, just as soon as it was well established, began to teach that the kingdom was in reality to appear at the culmination of the Christian age, at the second coming of Christ. (170:5.12)
His apostles and disciples most certainly linked these two teachings together. When the kingdom failed to materialize as they had expected, recalling the Master's teaching concerning a future kingdom and remembering his promise to come again, they jumped to the conclusion that these promises referred to an identical event; and therefore they lived in hope of his immediate second coming to establish the kingdom in its fullness and with power and glory. And so have successive believing generations lived on earth entertaining the same inspiring but disappointing hope. (170:4.16)
Sooner or later another and greater John the Baptist is due to arise proclaiming "the kingdom of God is at hand"--meaning a return to the high spiritual concept of Jesus, who proclaimed that the kingdom is the will of his heavenly Father dominant and transcendent in the heart of the believer--and doing all this without in any way referring either to the visible church on earth or to the anticipated second coming of Christ. There must come a revival of the actual teachings of Jesus, such a restatement as will undo the work of his early followers who went about to create a sociophilosophical system of belief regarding the fact of Michael's sojourn on earth. In a short time the teaching of this story about Jesus nearly supplanted the preaching of Jesus' gospel of the kingdom. In this way a historical religion displaced that teaching in which Jesus had blended man's highest moral ideas and spiritual ideals with man's most sublime hope for the future--eternal life. And that was the gospel of the kingdom. (170:5.17)
The gospel of the kingdom, the message of Jesus, had been suddenly changed into the gospel of the Lord Jesus Christ. They now proclaimed the facts of his life, death, and resurrection and preached the hope of his speedy return to this world to finish the work he began. Thus the message of the early believers had to do with preaching about the facts of his first coming and with teaching the hope of his second coming, an event which they deemed to be very near at hand. (194:4.5)
"But the times of the reappearing of the Son of Man are known only in the councils of Paradise; not even the angels of heaven know when this will occur. However, you should understand that, when this gospel of the kingdom shall have been proclaimed to all the world for the salvation of all peoples, and when the fullness of the age has come to pass, the Father will send you another dispensational bestowal, or else the Son of Man will return to adjudge the age."(176:2.5)