If he forgives then why does he also punish?
If G-d is merciful and he does not punish, how do believers get justice?
He forgives the Muslims that ask for forgiveness. Allah is merciful to those that believe in Him. If you don't believe in Him and his Message, then you will be one of those that are punished, hence this is one of the reasons why punishment is needed. We are not perfect, and we are made to be sinful so that we repent and kill our arrogance.
The question is: If somebody commits a crime and G-d is merciful, how does the victim of the crime receive justice?
Through sincere repetance of that particular sin.
On the day of Judgement, our deeds are weighed and our sins are weighed. There may be sins that we have not repented for, as we do not keep track of what we have sinned and what we have repented for. For someone to be forgiven for everything, he would have to repent for every single sin. Would you be able to remember every sin that you have commited from the day you hit puberty? Would you also be able to know which sins Allah forgave you for and which He didn't? There are even times that we are unaware where Allah will forgive all of our sins, but yet we are still commanded to repent.
Many a times, when one sins, lets say they commited zina (unlawful sex), they will repent for having unlawful intercourse, but they may forget all the sinning that led up to that, e.g. lowering the gaze, dressing modestly, being alone with a nonmahrem, etc.
The second way we are judged, is by our intentions:
Narrated ‘Abdullâh bin ‘Abbâs : Allah’s Messenger said that Allah the Glorious said, “Verily, Allah has ordered that the good and the bad deeds be written down. Then He explained it clearly how (to write):He who intends to do a good deed and he does not do it, then Allah records it for him as a full good deed, but if he carries out his intention, the Glorious and the Great Allah writes it down for him with Him as from ten to seven hundred times, and even many times more. But if he intends to do an evil act and has not done it, then Allah writes it down with Him as a full good deed, but if he intends it and has done it, Allah writes it down as one bad deed. (Al-Bukhâri and Muslim)
Punishment is also a drive to repent, like a warning. It reminds us that we are not perfect and that we will be punished for our sins. If always kept in thought that Allah is just merciful and He will forgive us for our sins, then we will continue to commit sins? right? Among believing that Allah is merciful, we too have to enstill in our hearts the fear of Allah's punishment and that Allah is also All-Knowing, All-Powerful, and Just.
We are not just punished in the afterlife, we may also be punished during life with tribulations that we are unaware of being a punishment. This may lighten our punishment in the hereafter.
In essence, as Muslims it should be not of importance to know whether we were forgiven for a sin, or rewarded for a deed, but rather that we strive to do the deed and refrain from commiting the sin. Allah is Just so we put our full trust in Him when the day of Judgment arrives.
Remember two things and forget one: Remember
Allah and your
death; and forget your
good deeds. -Luqmaan (radiallahu 'anhu)
