The basic goal of i’tikaaf – why have the Muslims forsaken this Sunnah?
Question

                Why have the Muslims forsaken i’tikaaf, even though it is the Sunnah of the Prophet (peace and blessings of Allaah be upon him)? What is the purpose of i’tikaaf?.
Praise be to Allah.Firstly: 
I’tikaaf is one of the confirmed Sunnahs which the Prophet (peace and blessings of Allaah be upon him) did regularly. 
See the evidence for its being prescribed in the answer to question no. 48999. 
This Sunnah has disappeared from the lives of the Muslims apart from those on whom Allaah has mercy. It is like many Sunnahs which the Muslims have virtually forsaken. 
There are several reasons for this, including the following: 
1-Weakness of faith in many hearts
2-Increased focus on worldly pleasures and desires, which leads to an inability to keep away from them even for a short time.
3-Lack on interest in Paradise on the part of many, and their inclination towards leisure and relaxation, so that they do not want to put up with the hardship of i’tikaaf even for the sake of earning Allaah’s pleasure.
Whoever understands the significance of Paradise and the greatness of its delights will sacrifice his life and that which is most precious to him in order to attain it. The Prophet (peace and blessings of Allaah be upon him) said: “The reward of Allaah is precious, the reward of Allaah is Paradise.” Narrated by al-Tirmidhi and classed as saheeh by al-Albaani, 2450.
4-Many people pay lip-service to the love of the Prophet (peace and blessings of Allaah be upon him), without acting upon it and implementing various aspects of the Sunnah, including i’tikaaf. Allaah says (interpretation of the meaning):
“Indeed in the Messenger of Allaah (Muhammad) you have a good example to follow for him who hopes for (the Meeting with) Allaah and the Last Day, and remembers Allaah much”
[al-Ahzaab 33:21]
Ibn Katheer said (3/756):
This verse represents a major principle: that we should follow the example of the Messenger of Allaah (peace and blessings of Allaah be upon him) in word and deed in all situations. 
Some of the salaf (early generations of Islam) found it odd that people did not observe i’tikaaf even the Prophet (peace and blessings of Allaah be upon him) persisted in doing so. Ibn Shihaab al-Zuhri said: It is strange that the Muslims have given up i’tikaaf when the Prophet (peace and blessings of Allaah be upon him) did not give it up from the time he entered Madeenah until Allaah took him (in death). 
Secondly: 
The i’tikaaf which the Prophet (peace and blessings of Allaah be upon him) always observed at the end of his life is i’tikaaf during the last ten days of Ramadaan. These few days may indeed be regarded as an intensive course of spiritual education which brings immediate positive results in a person’s life during the days and nights of Ramadaan and in the coming days, until the next Ramadaan comes. 
How great is the Muslims’ need to revive this Sunnah and establish it in the proper manner, as the Messenger of Allaah (peace and blessings of Allaah be upon him) and his companions used to observe it. 
How great will be the success of those who adhere to the Sunnah after the ummah has neglected it and become corrupt.  
Thirdly: 
The basic goal of the Prophet’s i’tikaaf was to seek Laylat al-Qadr. 
Muslim (1167) narrated that Abu Sa’eed al-Khudri (may Allaah be pleased with him) said: The Messenger of Allaah (peace and blessings of Allaah be upon him) observed i’tikaaf during the first ten days of Ramadaan, then he observed i’tikaaf during the middle ten days in a small tent at the door of which was a reed mat. He took the mat in his hand and lifted it. Then he put his head out and spoke to the people, and they came close to him. He said: “I observed i’tikaaf during the first ten days seeking this night, then I observed i’tikaaf during the middle ten days. Then someone came and said to me that it is in the last ten days, so whoever among you wishes to observe i’tikaaf let him do so.” So the people observed i’tikaaf with him. 
This hadeeth teaches us a number of things: 
1-That the basic goal of the i’tikaaf of the Prophet (peace and blessings of Allaah be upon him) was to seek Laylat al-Qadr and to prepare to spend that night in worship. That is because of the great virtue of that night of which Allaah says (interpretation of the meaning): “The Night of Al‑Qadr (Decree) is better than a thousand months (i.e. worshipping Allaah in that night is better than worshipping Him a thousand months, i.e. 83 years and 4 months)” [al-Qadr 97:3].
2-The Prophet (peace and blessings of Allaah be upon him) strove to seek that night before he was told when it is. So he started with the first ten days, then he observed it during the middle ten, then he continued to observe i'tikaaf during the last ten days, when he was told that it is in the last ten days. This is the utmost effort to seek Laylat al-Qadr.
3-The Sahaabah (may Allaah be pleased with them) followed the Messenger of Allaah (peace and blessings of Allaah be upon him), because they started i’tikaaf and continued with him until the end of the month, because they were so keen to follow his example.
4-The Messenger of Allaah (peace and blessings of Allaah be upon him) was compassionate towards his companions and showed mercy to them, because he knew that i’tikaaf was difficult for them. So he gave them the choice between staying with him or of leaving, and said: “…so whoever among you wishes to observe i’tikaaf let him do so.”
There are other aims of i’tikaaf as well, including the following: 
1-Being alone with Allaah and cutting oneself off from people if possible, so that one may focus completely on Allaah.
2-Renewing oneself spiritual by focusing totally on Allaah.
3-Cutting oneself off completely in order to worship Allaah with prayer, du’aa’, dhikr and reading Qur’aan.
4-Protecting one’s fast from everything that may affect it of whims and desires.
5-Reducing permissible worldly pleasures and refraining from many of them even though one is able to enjoy them.
See al-I’tikaaf Nazrah Tarbawiyyah by Dr. ‘Abd al-Lateef Balto.