Praise be to Allah.
There are three reasons why praying istikhaarah is important:
The first reason is to show our desperate need of Allah alone, to disconnect any hope except hope in Allah, to put our trust in Him (may He be glorified and exalted), and to delegate all our affairs to Him. All of these are sublime aspects of Tawheed and Islam, which praying istikhaarah helps one to attain and helps one to establish them, especially for the one who gets used to doing it often and realizes and understands in his heart its importance and the wisdom behind its being prescribed.
The second reason is to make the right choice, be successful in what one is striving to achieve and to be helped by Allah in one’s efforts. Whoever delegates his affairs to Allah, He will suffice him, and whoever asks of Allah with sincerity, He will grant his need and not withhold it.
Al-Ghazaali says in Ihya’ ‘Uloom ad-Deen (1/206):
Some wise men say that whoever is inspired to do four things will not be deprived of four things: whoever is inspired to give thanks will not be deprived of more [of Allah’s bounty]; whoever is inspired to repent will not be deprived of his repentance being accepted; whoever is inspired to pray istikhaarah will not be deprived of a good outcome; and whoever is inspired to seek the advice of others will not be deprived of reaching the right decision. End quote.
With regard to the hadith, “He will not be disappointed who prays istikhaarah, and he will not regret it who seeks the advice of others,” this is a fabricated (mawdoo‘) hadith. See: as-Silsilah as-Saheehah (611) by Shaykh al-Albaani.
The third reason is acceptance of the divine decree and contentment with one’s lot. Whoever seeks Allah’s guidance in his affairs by praying istikhaarah will not regret what he ultimately chooses to do, and he will feel reassurance and certainty which will ward off from him all worry and grief that could result from his choice. This reason is one of the greatest benefits that one could attain through praying istikhaarah.
Ibn Abi’d-Dunya narrated in ar-Rida ‘an Allah bi Qada’ihi (92) and elsewhere, with his isnaad from Wahb ibn Munabbih, that he said:
Daawood (peace be upon him) said: O Lord, which of Your slaves is most hateful to You? He said: A slave who prayed to Me for guidance [istikhaarah] concerning something, and I chose for him, but he was not content with it. End quote.
Ibn al-Qayyim (may Allah have mercy on him) said in al-Waabil as-Sayyib (157):
Shaykh al-Islam Ibn Taymiyah used to say: He will never regret it who prays istikhaarah seeking the guidance of the Creator and who seeks advice from people, then remains steadfast in whatever decision he makes. End quote.
Ibn al-Qayyim mentioned these words of wisdom and these benefits in a brilliant discussion of the importance of praying istikhaarah, and he said – as we see in Zaad al-Ma‘aad (2/442):
He compensated them with this supplication – the du‘aa’ of istikhaarah – which reflects the concept of Tawheed, desperate need of Allah’s help, servitude to Him, putting one’s trust in Him and seeking help from the One in Whose hand is all goodness, for no one could grant all that is good except Him, and no one can avert all that is bad except Him, for He is the One Who, if he opens the door of mercy to His slave, no one will be able to withhold it from him except Him, and if He withholds [mercy], no one will be able to make it reach him by any means, such as augury [bird omens], astrology, horoscopes and the like. This supplication [istikhaarah] is the “good omen” of the blessed and guided, for whom Allah has already decreed the best reward, and it is not the “omen” of the people of shirk, doom and failure, who associated other gods with Allah; but they will come to know.
This supplication [istikhaarah] implies affirmation of the existence of Allah (may He be glorified); affirmation of His perfect attributes, such as His perfect knowledge, power and will; affirmation of His Lordship, delegating one’s affairs to Him, seeking His help, putting one’s trust in Him, turning away from relying on one’s own means, declaring that there is no power and no strength except with Him, acknowledging one’s failure to know what is good for oneself and to attain it, and acknowledging that that is all in the hand of one’s Protector, Creator and true God. In Musnad al-Imam Ahmad, it is narrated from Sa‘d ibn Abi Waqqaas that the Prophet (blessings and peace of Allah be upon him) said: “The sign that the son of Adam is blessed is that he seeks guidance from Allah [istikhaarah] and accepts what Allah decrees, and the sign that the son of Adam is doomed is that he does not seek guidance from Allah [istikhaarah] and is discontent with what Allah decrees.”
Think about how what Allah decrees comes in between two things: putting one’s trust in Him, which is the essence of istikhaarah, before His decree comes to pass, and being content with what Allah decrees after it comes to pass. These two are the essence of being blessed. The essence of being doomed is that [what Allah decrees] is preceded and followed by a failure to put one’s trust in Him and seek His guidance [istikhaarah] before His decree comes to pass, and discontent after it comes to pass.
So putting one’s trust in Allah comes before the decree comes to pass, then when it comes to pass, true servitude to Him should be demonstrated by showing contentment afterwards, as it says in al-Musnad. An-Nasaa’i added in the famous supplication: “…and I ask You for contentment after the decree comes to pass.”
This is of a higher level than simply being content with the divine decree, because a person may have resolve [to be content with it], but when the decree comes to pass, he loses his resolve. So if a person attains contentment after the decree comes to pass, that is a very high status.
The point is that istikhaarah is putting one’s trust in Allah, delegating one’s affairs to Him, swearing an oath by His power and knowledge, and trusting Him to make a good choice for His slave. This is the requirement that is needed to show that one is content with Allah as Rabb (Lord), and a person will not have the taste of faith if he is not like that. If he is content with the decree after it comes to pass, then that is a sign that he is blessed. End quote.
And Allah knows best.