Them!! specially the monks and priest who spread and teach things.

When asked by the Pharisees when the kingdom of God would come, Jesus replied, “The kingdom of God will not come with observable signs. 21Nor will people say, ‘Look, here it is, or ‘There it is. For you see, the kingdom of God is in your midst. 22Then He said to the disciples, “The time is coming when you will long to see one of the days of the Son of Man, but you will not see it.…

The coming of the kingdom of god (aka heaven) to people's world. Or people go to the heaven is a same thing.
The result is same that is people want to enter the heaven.

So whether it's in people's life or after life. They will not see it(heaven). Your god said it explicitly.
And it not means the the earth will transform into heaven. It's a viewpoint of other people but The god said it won't be observable so there won't be any difference.

So the speech of people go to heaven after life is just a lie.
Because
1. When god is on the earth. People want to go to heaven in their life rather than after life.
2. When god is not on earth. People might want to go to heaven in their after life.

Whatever it is, it won't be achieveable.

And I never met or see some christian said that god will not save your or you won't be able go to heaven just because you believe in god.
So people they all lied.