Importance of Istikharah
Question

May I ask you this question? I want to put my mind at rest, because many people suffer from these intrusive thoughts, so my question will also benefit many people who read it. We often hear about praying Istikharah, but we only do it on rare occasions. We may pray when there is doubt in our hearts, because we do not know how important it is. Sometimes it crosses our minds that the decree of Allah is what is going to come to pass, so what is the point of asking and offering supplication and striving? Please tell me about praying Istikharah.
Praise be to Allah.Istikhaarah: A Manifestation of Tawhid and Trust in Allah
There are three reasons why praying Istikharah 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 Tawhid and Islam, which praying Istikharah 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.

Divine Assistance and Successful Decision-Making

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-Ghazali (may Allah have mercy on him) says in Ihya’ `Ulum Ad-Din (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 Istikharah 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 Istikharah, and he will not regret it who seeks the advice of others,” this is a fabricated Hadith as stated by Shaykh Al-Albani in As-Silsilah As-Sahihah (611)
Contentment with Allah’s Decree: The Essence of Istikhaarah

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 Istikharah 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 Istikharah.

Ibn Abu Ad-Dunya (may Allah have mercy on him) narrated in Ar-Rida `an Allah bi Qada’ihi (92) and elsewhere, with his chain of narration from Wahb ibn Munabbih, that he said:
Dawud (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 [Istikharah] 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-Wabil As-Sayyib (157):
Shaykh Al-Islam Ibn Taymiyah (may Allah have mercy on him) used to say: He will never regret it who prays Istikharah 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 (may Allah have mercy on him) mentioned these words of wisdom and these benefits in a brilliant discussion of the importance of praying Istikharah, and he said – as we see in Zad Al-Ma`ad (2/442):
He compensated them with this supplication – the Du`a of Istikharah – which reflects the concept of Tawhid, 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 [Istikharah] 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 [Istikharah] 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 Abu Waqqas (may Allah be pleased with him) 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 [Istikharah] and accepts what Allah decrees, and the sign that the son of Adam is doomed is that he does not seek guidance from Allah [Istikharah] 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 Istikharah, 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 [Istikharah] 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-Nasa’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 Istikharah 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.