What is the clear and comprehensive meaning of the word "Qadar" (divine decree)? Are illnesses resulting from sin, such as fornication, considered Qadar? Is marriage Qadar, even though the Messenger commanded choosing a wife? Is the profession I work in Qadar, or is it a result of diligence and hard work?

Belief in Divine Decree (Qadar), both its good and bad, is a fundamental pillar without which a person's faith is not complete, as attested by the words of Gabriel (peace be upon him) to the Prophet Muhammad (peace be upon him), and by numerous Quranic texts that affirm everything is created by decree.

Everything that happens to a person, including striving to find a job or choosing a wife, is part of Allah's decree. Both causes and effects are by Allah's decree.

The Prophet (peace be upon him) encouraged choosing a righteous wife, emphasizing that religion is the most important criterion, and urged choosing good lineages and selecting competent partners.

A Muslim must be certain that whatever befalls them is by Allah's decree, and that no one can change what Allah has decreed for or against them. However, this does not mean predestination (Jabriyyah), as a person possesses will and ability with which they choose their actions, and Allah Almighty knew what would be, so He recorded it.

A servant must strive to acquire lawful means in seeking sustenance and marriage, and among the most important of these are steadfastness in Allah's religion and abandoning sins. For, seeking forgiveness and piety bring sustenance, relief, and ease.

Furthermore, sins and acts of disobedience have a negative impact; they may deprive a person of sustenance and cause them calamities and illnesses, such as deadly diseases that spread with the prevalence of immoral acts.

It is not necessary that every man is destined to marry; some men may die before marriage, and there are famous scholars who died unmarried.