‘Aqeedah is that which the heart is firm about and in which there is no doubt. The word “‘aqeedah” is derived from its root ‘aqada which means “being firm, certain, confirmed” etc. Therefore, the theology of any religion is ‘aqeedah.
The Islamic ‘aqeedah, however, is the belief in tawheed (oneness of Allah in all its three categories, namely tawheed ar-rububiyyah tawheed al-asma’ was-sifaat and tawheed al-‘ibadah or al-uloohiyyah), the Prophets, the books, the angels, the Last Day and qadr (destiny), as it is known from Qur’ân and the authenticated Sunnah.
Even though the word “‘aqeedah” is not mentioned in the Qur’ân, we find several explanations of the Islamic ‘aqeedah in the Qur’ân and the Sunnah.
The importance of ‘aqeedah is seen in several ayaat and some ahaadeeth.
As a Muslim, the very first thing to be firm upon is the statement “laa ilaaha illAllaah wa Muhammadur RasoolUllaah” as it is the first pillar if Islam. When Islam was revealed to the Prophet Muhammad, he first called to the correct ‘aqeedah.
"The Messenger has believed in what was revealed to him from his Lord, and [so have] the believers. All of them have believed in Allah and His angels and His books and His messengers, [saying], "We make no distinction between any of His messengers." And they say, "We hear and we obey. [We seek] Your forgiveness, our Lord, and to You is the [final] destination." (2:285)
Therefore, ‘aqeedah is the basis of our complete faith and all our deeds. All deeds depend on ‘aqeedah and without the correct ‘aqeedah, all deeds have no benefit. This is because Allah says in the Qur’ân:
“That is the guidance of Allah by which He guides whomever He wills of His servants. But if they had associated others with Allah , then worthless for them would be whatever they were doing.” (6:88)
“And it was already revealed to you and to those before you that if you should associate [anything] with Allah, your work would surely become worthless, and you would surely be among the losers." (39:65)
Because deeds are dependent on the correct 'aqeedah the Prophet remained in Makkah for 13 years and the revelation was restricted to ‘aqeedah only (except prayer). Only after the correct ‘aqeedah was established in the hearts of the Muslims, the shari’ah was revealed and established.
Moreover, comprehensive knowledge about ‘aqeedah is tremendous for our faith as it protects us from shirk, as Allah says in the Qur’ân:
“And most of them believe not in Allah except while they associate others with Him.” (12:106)
‘Aqeedah is the most important principle in Islam, as all deeds are dependent on the correct ‘aqeedah. It helps us knowing our Creator and how to worship Him properly. Entering paradise is, therefore, dependent on the correct ‘aqeedah as well. Comprehensive knowledge about the Islamic ‘aqeedah protects us from going astray and teaches us why other religions (and sects) are deviant.