Justice in light of destiny
Excellent and common question (misconception). So lets begin.
Let me clarify you CHOSE to come here as explained in Surah al-Araaf:
172 And (remember) when your Lord brought forth from the Children of Adam, from their loins, their seed (or from Adam's loin his offspring) and made them testify as to themselves (saying): "Am I not your Lord?" They said: "Yes! We testify," lest you should say on the Day of Resurrection: "Verily, we have been unaware of this."
173 Or lest you should say: "It was only our fathers afortime who took others as partners in worship along with Allah, and we were (merely their) descendants after them; will You then destroy us because of the deeds of men who practised Al-Batil (i.e. polytheism and committing crimes and sins, invoking and worshipping others besides Allah)?" (Tafsir At-Tabari).
You and I don't remember testifying ourselves to our Lord Allah and thus this makes this life a test ([He] who created death and life to test you [as to] which of you is best in deed - and He is the Exalted in Might, the Forgiving [67:2]). But if we obey we are above angels, and if we disobey we are worse than pigs.
Destiny (whether you end up in Hellfire or Paradise) is further clarified by this Hadith:
'Ali reported that one day Allah's Messenger (may peace be upon him) was sitting with a wood in his hand and he was scratching the ground. He raised his head and said: There is not one amongst you who has not been allotted his seat in Paradise or Hell. They said: Allah's Messenger. then, why should we perform good deeds, why not depend upon our destiny? Thereupon he said. No, do perform good deeds, for everyone is facilitated in that for which he has been created; then he recited this verse:" Then, who gives to the needy and guards against evil and accepts the excellent (the truth of Islam and the path of righteousness it prescribes), We shall make easy for him the easy end..." (xcii. 5-10).
The test is to believe and follow Allah without seeing Him. Thus he sent messengers and books (quran, bible, torah etc). For this the following verse is relevant: Verily,, those who fear their Lord unseen (i.e. they do not see Him, nor His punishment in the Hereafter), theirs will be forgiveness and a great reward (i.e. Paradise).[67:12]
Right now your aim to obey Allah and His messenger in totality as you don't have any option. Here this verse is relevant:
It is not for a believer, man or woman, when Allah and His Messenger have decreed a matter that they should have any option in their decision. And whoever disobeys Allah and His Messenger, he has indeed strayed into a plain error.[33:36]
The Quran beautifully explains the paths in Surah Balad:
7 Does he think that none sees him?
8 Have We not made for him two eyes,
9 And a tongue and two lips?
10 And shown him the two ways (good and evil)?
You will remember that you testified to Allah when you are resurrected from the dead and He will tell you what you used to do.
There will be NO ONE WHO WILL COMPLAIN OF INJUSTICE as stated in the verse:
And whoever does righteous good deeds, male or female, and is a (true) believer [in the Oneness of Allah (Muslim)], such will enter Paradise and not the least injustice, even to the size of a speck on the back of a date-stone, will be done to them. [4:124]
You must be confused right now, right? So lets get it straight what the disbelievers (someone who rejects the message-kafir) will say in hellfire in Surah Mulk:
6 And for those who disbelieve in their Lord (Allah) is the torment of Hell, and worst indeed is that destination.
7 When they are cast therein, they will hear the (terrible) drawing in of its breath as it blazes forth.
8 It almost bursts up with fury. Every time a group is cast therein, its keeper will ask: "Did no warner come to you?"
9 They will say: "Yes, indeed a warner did come to us, but we belied him and said: 'Allah never sent down anything (of revelation); you are only in great error.'"
10 And they will say: "Had we but listened or used our intelligence (notice you are encouraged to use your intelligence and hearing), we would not have been among the dwellers of the blazing Fire!"
11 Then they will confess their sin. So, away with the dwellers of the blazing Fire!
Since they will confess their sins how is it possible that injustice is done to them?
Indeed the warner sent to us was Prophet Muhammad (pbuh) who is mentioned in the same Surah:
21 Who is he that can provide for you if He should withhold His provision? Nay, but they continue to be in pride, and (they) flee (from the truth).
22 Is he who walks prone (without seeing) on his face, more rightly guided, or he who (sees and) walks upright on the Straight Way (i.e. Islamic Monotheism)?
23 Say it is He Who has created you, and endowed you with hearing (ears) and seeing (eyes), and hearts. Little thanks you give.
24 Say: "It is He Who has created you on the earth, and to Him shall you be gathered (in the Hereafter)."
25 They say: "When will this promise (i.e. the Day of Resurrection) come to pass if you are telling the truth.?"
26 Say (O Muhammad صلى الله عليه وسلم): "The knowledge (of its exact time) is with Allah only, and I am only a plain warner."
27 But when they will see it (the torment on the Day of Resurrection) approaching, the faces of those who disbelieve will change and turn black with sadness and in grief and it will be said (to them): "This is (the promise) which you were calling for!"
28 Say (O Muhammad صلى الله عليه وسلم): "Tell me! If Allah destroys me, and those with me, or He bestows His Mercy on us - who can save the disbelievers from a painful torment?"
29 Say: "He is the Most Gracious (Allah), in Him we believe, and in Him we put our trust. So you will come to know who it is that is in manifest error."
30 Say (O Muhammad صلى الله عليه وسلم): "Tell me! If (all) your water were to sink away, who then can supply you with flowing (spring) water?
The current Orator Dr. Zakir Naik himself challenges other beliefs because he knows Islam is the truth, and no one has yet been able to do. Do you know why? Their religious scriptures teach the same (prophecy of Prophet Muhammad (pbuh) and oneness of Allah). Lets take Holy Bible as an example:
Prophecy about the Last Messenger Muhammad (pbuh): "I have many more things to say to you, but you cannot bear them now. 13"But when He, the Spirit of truth, comes, He will guide you into all the truth; for He will not speak on His own initiative, but whatever He hears, He will speak; and He will disclose to you what is to come.…[16:12]
Oneness of Allah and Jesus (ra) as messenger: For there is one God and one mediator between God and mankind, the man Christ Jesus,[timothy 2:5]
I thank Allah for the knowledge and the life test He gave me. Verily to Him is my return and inshallah paradise shall be our abode.