After Life

i dont really know the akhirah/dunya point of view of Judaism.

but arent Christians also about the next life and ...ouch...im confused. they are already going to heaven because Jesus ('alaihissalaam) died for them? but they should be grateful for this all their lives? (hence the people who arent grateful go to Hell?) is this how it works?

Is it true? Is it kind? Is it necessary?