We test you with Evil and with good as a trial (Surah Anbiya, verse 35)

From the five pillars of Emaan, Qadar is one of them and many people understand Qadar as destiny. So believing in Qada and Qadar is a part of faith. In Islam, "predestination" is the usual English language rendering of a belief that Muslims call al-qaḍāʾ wa al-qadr. The phrase means "the divine decree and the predestination." Qada means, Allah has decided and written down everything that is going to happen, thousands of years before creating the world. This includes, even the gender of each child that is born, every leaf that falls, the landing place of every drop of rain  is recorded before Allah created the universe. Thus deciding of the entire creation’s acts is called Qada and from this root word we have the word ‘Qadi’ which means one who delivers a decision and the court where such decisions are given are known as ‘ Darul Qada.’ Therefore we believe that Allah has decided about each and everything that exists according to His supreme wisdom.

Allah has decided each thing as per his complete knowledge. He knows best who should he give wealth and who should be deprived of it. He has created everything in a right proportion and its distribution is also decided. This is known as Qadr. There the combined meaning of Qada and Qadr is called taqdeeer. The importance of believing in Taqdeer is found in many verses of Qur’an and Hadith e Jibrael. Allah sent Jibrael to teach the Muslims about Emaan and Taqdeer was a part of that lesson. The way we believe in the existence of Allah, His Messengers, His books, His Angels, The Day of Judgement, similarly, we are supposed to believe in Taqdeer too.