Many have said that we have more references in the Bible to Jesus talking about hell, fire, punishment, judgement etc than we do about Heaven and eternal life.
I haven't done the count for myself as to the exact numerical difference in references, but suffice to say that Jesus talked quite a lot about the subject as a warning to people.
If Jesus felt the need to warn people about it, why wouldn't someone preaching in his name do the same?
Does Jesus also talk about the love of God? Yes. He is the walking embodiment of it. Yet in Revelation we see Jesus will be returning with a sword and his robe dipped in blood, to execute righteous vengeance on the earth. Revelation 19:11-20 We see the judgement of God embodied in Jesus's second coming.
What do we see in the prophets? Warning of judgement, and the consequences. Even reference to the ultimate judgement God will bring at the end, where wrath is poured out on all the evil nations of the world.
Daniel 12:2 would be a clear reference to the fact that this judgement has eternal ramifications.
Do the prophets also talk about the love of God? Yes. In fact, it was because Jonah knew God was so good and loving that he refused to preach a warning of judgement to Ninevah because he didn't want that evil city to repent and be spared from wrath (Jonah 4:2). It is the goodness of God that is meant to bring us to repentance (Romans 2:4). To someone who has spurned the goodness of God and taken it for granted, a warning of judgement becomes necessary - and even then we see in the Bible they don't always heed it
The warning of judgement, if done with the right heart, is itself an act of love meant to turn someone away from destruction.
Because it was a medieval creation?
No, it's not. Aside from the fact that the concept is clearly expressed in the new testament itself, which we know goes back long before that time period; We can see the concept vividly detailed in the apocryphal writings we've recovered from both before and not long after the time of Christ - The Book of Enoch (2nd century BC) and the Apocalypse of Peter (2nd century AD).