What is your understanding on heaven or the afterlife? Is there a punishment waiting for some and paradise for others and if so what would you say is necessary to receive paradise and can there be an assurance of receiving it?
(note : like your questions)
You know this is one of the three basis of Islam (Monotheism + Prophecy (as in Prophets, not TT killing stuff) + Judgement Day)
so it is not a small subject.
1- There are 5 sections of life : A- World of (sprinking - means of creating) where Allah made the human being a monotheist in nature. B- this world where the human gets a body to change the power he/she was given in the first world to act C- World Of Barzakh (which is where dead people are until death and in this world the (Nafs) - which is the thing sprinkled - is tortured as in the much it is freed from the attachment to the second world, so to be ready for the next section D- Judgement Day : a mental (philosophical mind - which is the power of the Nafs) judgement where everyone is given what they deserve, one of the known Islamic traditions is that humans are to be changed to monsters according to their "highest power", those who are judged as humans are those close to Allah E- Afterlife : the life according to what was the human judged to in Judgement day.
2- Afterlife is of two parts Hell and Heaven, it doesn't mean that Hell is fire, maybe it is not, it would be according to what is considered as a torture for this specific person, And they are not YES or NO, they are relative with degrees (which is reasonable because people are relative to each other from manners belief .. etc).
this is controlled by two (scores) : 1- Thawab : repayment 2- Dhanb : Sin. the more you get from the first the more you go up, the less you get from the second you go down.
The Highest part of heaven is where Prophets and Messengers are.
3- I am going to make this as rules so it would be easier :
Rule One : You will be Judged on your mind, if you even had a small doubt that Atheists have the right and didn't go after that doubt Allah would judge you why didn't you understand the place of your suspicion ?
Rule Two : People of Science are judged, but those of ignorance aren't means if an ordinary Muslim or Christian or Buddhist who just did what he was brought up to do without thinking whatsoever about other theologies, don't have no "repayment" nor "sin", they are just in a place in Paradise. but they are not as the Scientist who known Allah and works to worship him.
Rule Three : if someone got after his doubt and became an Atheist and it really REALLY (means within himself not what he says to people) believed that, he is not going to be thrown to Hell, he's just like the ignorant or maybe better because he made Jihad to know God but couldn't find him.
Rule Four : if a cleric (scientist) , Muslim or Christian was raised on his religion and his mind didn't accept anything but his book, and his mind didn't get doubted for other theologies, then he would be judged as how sincere was he to God.
Rule Five : Who goes to Hell are those who have the doubt in Islam and say "Maybe Islam is right" and then go after their doubt and find Islam is Right but don't become Muslims, those are to stay in hell forever.
Rule Six : The Relativity stays, a cleric who kills people will be judged for that, and according to whatever measurements Allah (the merciful) put on that day this cleric will be judged, means to his daily life and what did he do in it, away from theology.
Usually who kills a soul without a right should be kicked really downstairs and stay there if not forever, for a very long time.
Rule Seven : We don't know whether we are right or wrong, so Allah knows who will go to Heaven and who will not. so we don't give Judgements.
Rule Eight : Personal Daily life sins are to be judged with "Barzakh life" torture or temporary torture in Hell, there are sins called "the great sins" , clerics have got split about it, if a muslim does one of them some say he stay forever in Hell and some say just for long time, and some say this is also about Ahlu-ul-Kitab (Christians and Jews) they would be tortured temporarily for not believing in Muhammad and then sent back to Heaven (if non of the rules up is applied on them)
Before you question :
1- I brought this from a book of Imam Khomeini (Mercy be upon his sacred soul) and from hearing a known Iraqi cleric man called Ayatullah Al-Haydari. although it is my words and my way of summarizing it.
2- What about those Dawah children who go out like "Hey we told you, you are all going to hell", not that they are cleric or theologians, but they don't understand the meaning of "Iqamat Hujah" to put a reason to convert to Islam is intentional not of speech, means if no one of the ones hearing doubt, then they are not given the reason therefore they are not going to hell.
The Assurance is yourself and your own thinking of life, Golden Rule is if you have a doubt go after it.