As Allah is omniscient he created the universe and put certain laws in place which are predetermined and unchangeable. These lalws are for humans beings and are outside of a persons control ( e.g. genes passed down )
Belief in predestination is important because:
It shows Allahs omnipotence
The laws of the universe are for the benefit of humanity
It gives comfort to Muslims as everything is part of Allahs plan
Even though Allah knows everything that happens, humans still have freewill. Humans should try make choices that follow Allahs commands and not their desires
Allah sent his messengers so that we know what will is
For Sunni Muslims, praying at Laylat Al-qadr can change your destiny
For Shia Muslims, praying and intentions can change your destiny throughout your life
Ways al-qadr can be understood:
Allah knows everything because he created the universe
Allahs laws are beyond human control
Humans have free will and can choose to do certain things
Nothing happens without Gods permission
Human intentions and actions can impact Allahs will
Although humans cannot help the society they are born into (such as a crime ridden one) Allah will consider all of this on the day of judgement