But didn't Jesus die for the remission of all our sins? Jesus rendered the concept of sin and hell useless.

Personally, I'm agnostic and can't grasp the idea that an all-loving God will send his one and ONLY SON to die for our sins. Why not just forgive us all? No need to send someone to get beaten inhumanly to death.

Come to think of it, why would an all loving God burn at least 75% of the population in hell for all eternity. Not even the worse people that lived on earth deserves that.

The idea of eternal suffering in hell is not biblical, but teachings from other religions like greek and nordic mitologies, were wrongfully incorporated in the belief of christians, even though it has no biblical basis. According to the Bible, when a person dies, his existance is extinct, his soul doesn't go to hell or heaven, he just cease to exist, his thoughts perish with him. So Christ also, according to the Bible, spent 3 days dead, extinct, not in heaven nor in hell.

But in the Bible, Christ promissed that he will ressurrect all the dead when he comes back, the same way he was resurrected (had his existance brought back from nothing) he will bring back to existence all his faithful dead. In the first round of resurrection which, according to revelations, happens right after he comes back, all faithful dead will resurrect and will never die again, but live forever like Christ. But in the second round of resurection, which will happen 1000 years after the first one, all the people that belongs to the second round will go through judgment, and the ones that are not approved will receive the second death: they will be thrown in flames and die again. There is no such thing as eternal torture for sinners in the Bible, they will suffer the second death after being judged, and will cease to exist forever.

So if you see any pastor, priest or whatever, saying that a christian that just died recently is now already walking in heaven, just like all others that died before him are alive with him in heaven, he is just teaching something not biblical. They are all dead, extinct, and will remain dead until Christ comes back.

The faith of a christian is not about going to heaven in the form of a "soul" right after death for believig in Christ. This idea of a soul that, upon death, goes imediatly to paradise or "underworld" comes from greek/nordic/egyptian mitologies. The faith of a christian is about believing in the promisse that someday you will be resurrected from the dead and receive a new immortal body when Christ comes back. Knowing that, until this day comes, your existence will vanish and will remain extinct after you die.

If that is the case, how will Christ decide?

If he knows everything about everybody, it would be easy for him to decide who can and who can't be part of the first resurrection round upon his second arrival.

Will he resurrect anyone that doesn't believe in him?

If you're that easily able to have your beliefs compared to a series of mythologies, maybe it's time to take a long, hard look at your own. Why have you accepted this particular set as your own, and cast the others aside as mythology? Because you're (presumably) geographically in a place where it's a prevailing belief? If you had been born into a world and told Nordic beliefs were true, odds are everyone would be walking around praising Odin.

According to the bible:

1st resurrection -> only the faithful believers will take part, and they will not suffer the second death, but live forever.

2nd resurrection -> all others will take part, and for this one there will be a judgment, only the ones that are approved will also live forever, the ones that don't pass the judgment will receive the second death, and cease to exist.