If God exists, why is there so much suffering and evil in the world?

In Islam, the existence of suffering and evil in the world is not seen as evidence against the existence of God, but rather as a test and a means of spiritual growth and development for human beings. Muslims believe that Allah is merciful and compassionate, but also just and wise, and that He has a plan and purpose for everything that happens in the world, even if it is not always immediately apparent to us.

Free will:

Muslims also believe that human beings have been given free will and the ability to choose between right and wrong, and that it is our choices and actions that often lead to suffering and evil in the world. Additionally, Muslims believe that suffering and hardship can be a means of purification and atonement for sins, and that it can also serve as a reminder of the temporary nature of this life and the importance of seeking spiritual salvation.

One verse in the Quran that highlights the idea of free will and the consequences of our choices is:

"Whoever does righteousness, it is for his [own] soul; and whoever does evil, [does so] against it. And your Lord is not ever unjust to [His] servants." (Quran 41:46)

This verse emphasizes that each person is responsible for their own actions and choices, and that the consequences of those actions will ultimately affect their own soul. It also reassures believers that Allah is just and fair in his dealings with his servants.

Regarding the concept of suffering and hardship as a means of purification and atonement for sins, there is a hadith (recorded saying of the Prophet Muhammad) that states:

"No fatigue, nor disease, nor sorrow, nor sadness, nor hurt, nor distress befalls a Muslim, even if it were the prick he receives from a thorn, but that Allah expiates some of his sins for that." (Sahih al-Bukhari 5641)

This hadith highlights the idea that even the smallest forms of suffering or hardship can serve as a means of purifying one's soul and atoning for sins. It is a reminder to believers that hardships should be faced with patience and trust in Allah's plan, as they can ultimately lead to spiritual growth and a greater reward in the hereafter.

Qadr or divine destiny:

In Islam, the concept of qadr, or divine destiny, also plays a role in understanding the presence of suffering and evil in the world. Muslims believe that everything that happens in the world, both good and bad, is ultimately under the control of Allah, and that even our suffering and hardships have a purpose and meaning within the larger plan of Allah.

One verse in the Quran that speaks to the concept of qadr is:

"Say, 'Never will we be struck except by what Allah has decreed for us; He is our protector.' And upon Allah let the believers rely." (Quran 9:51)

This verse emphasizes the idea that everything that happens to us is ultimately under the control of Allah, and that believers should trust in Allah's plan and rely on Him for guidance and protection. It also implies that hardships and difficulties may be a part of Allah's decree, but that believers should remain steadfast in their faith and trust that everything is ultimately for their own benefit and the greater good.

One hadith that speaks to the concept of qadr is:

Narrated Abdullah ibn Amr: The Prophet (peace be upon him) said, "Allah has ordained measures (of mercy) for everything, so when you kill, kill in a good way and when you slaughter, slaughter in a good way. So every one of you should sharpen his knife, and let the slaughtered animal die comfortably." (Sahih Muslim 1955)

This hadith indicates that Allah has predetermined measures and decrees for everything, including acts of killing and slaughter. Muslims are encouraged to carry out these acts in a way that is merciful and compassionate, reflecting the idea that even in difficult or unpleasant situations, believers should strive to act in accordance with the divine will and plan of Allah.

Overall, Muslims believe that the existence of suffering and evil in the world is not evidence against the existence of God, but rather a part of the complex and mysterious nature of the world that Allah has created, and that our ultimate goal should be to seek guidance and strength from Allah in facing these challenges and striving towards spiritual growth and enlightenment.