In a single word - FEAR! In two words, apocalyptic fear, which was the fear that the world was going to end in the lifetime of the hearers of the warning.
As John the baptizer was warning to repent because the kingdom of God was at hand, Jesus likewise, when John was put in prison, (Mark 1:14) went preaching that the kingdom of God was at hand. They both warned of the wrath to come. Not only of the wrath to come, but that it was coming soon - it was "at hand" and in "this generation" at the time of their preaching their apocalyptic message.
Now, the Jews expected a Messiah at this time. Therefore, it seemed prudent to the Jews to heed such a warning or at least to listen to it. You know, just in case it may be true - why take a chance?
A man called Paul, coming on the scene following the deaths of John and Jesus, had a vision and a revelation of this soon coming kingdom of God himself and went all over the Roman world preaching his own message of this kingdom of God that was soon to come. Of course, messianic Jews had been way ahead of Paul and already had preached about a coming messiah. This was nothing new that Greek and Roman believers in Judaism had not already heard about. The messianic Jews had already paved the way for Paul to preach his own religion. Paul preached that the messiah they looked for had already came and was due to return at any time to judge the world. Anyone who wouldn't listen and convert to Paul's religion would be destroyed by the returning Christ.
Judgment day, which was already believed in all over the empire, was coming soon and all the unbelievers would be destroyed by fire in God's wrath and they only had a "short time" (1 Cor. 7:29). No time to waste - just as the writer of 1Peter 4:7 said, "the end of all things is at hand" and "the day of the Lord will come as a thief in the night; in the which the heavens shall pass away with a great noise, and the elements shall melt with fervent heat, the earth also and the works that are therein shall be burned up" (2 Pet. 3:10).
But, hey, we Christians don't have to worry, because there will be a new heavens and a new earth for the believers in Paul's religion of Christianity to live in (2 Pet. 3:13).
Now, all this was predicted to be "at hand" over 1,900 years ago and still people are accepting this story out of the fear that it may yet happen. And, that's how the Bible works, it works on people's FEAR. They fear to NOT believe it, no matter how silly it sounds to them in this modern age - after all, why chance it? But, why do they take their fear and call it love? Simple. They're afraid not to, they are simply afraid to let go of a 2,000 year old myth. They call it "love" because that sounds better to them than does "fear".
Can you really blame them though? After all, by the 4th century, unbelievers and other sinful people will be tortured in hell-fire for all eternity. What is and how long is eternity? Eternity is truly a meaningless word with no intelligible definition outside of a theological one, yet even the unintelligent think they know what it means.
In this one life we have, there are two paths a person may follow:
There is the broad path that most folks follow toward superstitious beliefs in the supernatural. There is a lot of advantage to this path, in that you will have a lot of company along the way, if you like clapping hands and singing praises to an invisible deity.
Then there is the narrow path toward actual knowledge based on facts and evidence. This is the correct path, in my opinion, and you may not have a lot of company. In fact, it can be pretty lonely, but there will be no superstitious fear to bind your life to deluded, religious fanatics trying to control even what and how you think.