Aqeedah is the creed, or belief system, of the Muslim. What we believe about Allah, his messenger, his angels, and the Qadr are all things that fall under the study of Aqeedah. Any Islamic belief you have that is not found in the Qur’an or Sunnah is a problematic belief.
Why is Aqeedah important?
I went to Ubayy b. Ka’b and said him : I am confused about Divine decree, so tell me something by means of which Allah may remove the confusion from my mind. He replied : were Allah to punish everyone in the heavens and in the earth. He would do so without being unjust to them, and were he to show mercy to them his mercy would be much better than their actions merited. Were you to spend in support of Allah’s cause an amount of gold equivalent to Uhud, Allah would not accept it from you till you believed in divine decree and knew that what has come to you could not miss you and that what has missed you could not come to you. Were you to die believing anything else you would enter Hell. He said : I then went to ‘Abd Allah b. MAs’ud and he said something to the same effect. I next went to Hudhaifah b. al-Yaman and he said something to the same effect. I next went to Zaid b. Thabit who told me something from the Prophet (May peace be upon him) to the same effect.
Aqeedah is important because having the wrong belief about Allah and what He revealed could land you in some serious trouble on the Day of Judgement.
In regards to learning about Aqeedah, this series by Tim Humble is a great place to start:
My latests posts on Aqeedah:
Hikmah Central 