Taken from Ghazi e Millat Hazrat Syed Hashmi Miya
It is an accepted fact among the Sunni and non-Sunnis that there are 3 questions in the grave.
First question: WHO IS YOUR GOD?
Second question: WHAT IS YOUR RELIGION?
Third question: WHAT DID YOU USE TO SAY ABOUT THIS MAN (Rasulullah sallallahu alayhi wa alihi wa sallam-who will come in the grave at the 3rd question with body and soul since the words of Hadith mentions rujul which means man, and man means a body and soul in it)
These 3 questions are in good order, read the note to the end, you'll know why.
The purpose for Munkir-Nakir to come in grave is to open the gate of either Paradise or Hell for the person. To know what this person deserves of these two gates, these 3 questions are asked.
First, who is your Rab? The moment you say Allah, it'll be proven than you were not a mushrik and idolator on earth, it'll be proven that you always believed in one Allah. But this is not sufficient, since even some jews and chritians too believed in one Allah.
Second question, what is your religion. Its already proven that you are a Muwahhid (believer in one Allah). But in order to know whether you are a muslim muwahhid or non-Muslim muwwahid, this second question is asked. The moment you say Islam, its proven that YOU CLAIMED to be muslim on earth. But even this is not sufficient to get you into Jannah. If this was enough, so why the 3rd question exist?? So claiming to be muslim on earth is not sufficient.
3rd question, what did you use to say about this man (Rasulullah sallallahu alayhi wa alihi wa sallam). This question is asked because among those who claimed to be muslims, 73 groups exist, of which only ONE will go to Jannah and the rest are in Hell. That's why, in order to know that to which group you belonged on earth, this question is asked. And its interesting that the 3rd question is asked about Nabi e Kareem RaoofurRaheem (sallallahu alayhi wa alihi wa sallam). This proves that the difference between the true group and the 72 fakes ones, is Ishq e Rasool (sallallahu alayhi wa alihi wa sallam). Only those who love him, only they have real Eemaan, and they will recognised him through the Light of their Eemaan. So, in this 3rd question Sunnis will become successful and the others will fail.
To be noted that the true translation of the 3rd question is [what you USED TO SAY about this man], this is the real translation. Many places it has been translated as [what DO YOU SAY about this man], this should be avoided.
So this is the first test. The second test is the questions of Judgement Day, the first question there will be asked about Namaz to Sunnis ONLY. Take the example of primary and secondary school. If you have failed in primary school, will you give examination in secondary school? Never. If you have failed in college, will you go to university? Never. So Grave is the first test, the test of Eemaan. If you have Eemaan, then you will have for the bigger test (Judgement Day). If you have failed in grave, so there's no other exam for you, you are going directly to Hell.
Grave is the test of Aqeedah & Eemaan and Judgement Day is the test of our Actions that we did on earth. If you don't have Eemaan, none of your actions ('aamal) are accepted, even if you prayed millions of Namaz. For example, hindus, even if they donate a mountain of gold in charity, this will not help them in Judgement Day because they don't have Eemaan itself. If you want your actions to be accepted, the condition is Eemaan. And no one's Eemaan is complete until he/she loves Rasulullah (sallallahu alayhi wa alihi wa sallam) more than everyone and more than himself/herself.
Based on these fact, we know that only Sunnis will give exam on Judgement Day because only Sunnis will be successful in the test of grave. The rest wahabis etc won't be needed on Judgement Day because they will fail the test of grave. These people will go directly to Hell. If you fail in grave, you wont be needed on Judgement Day. As example, take Grave as primary school test, and Judgement Day as secondary school test. AlHamdulillah all Sunnis will pass the first test, and all non-sunnis will fail in the first test.
May Allah give us the Shafa'at of His Beloved Sallallahu alayhi wa alihi wa sallam
Ya Rasulallah give us your Shafa'at for the sake of Allah and for the sake of your Aal (descendants)
Ameeen