The Islamic Creed is the creed that Allah sent all His Prophets with, revealed all His Books with, and obligated all His creation to believe in, both Mankind and Jinn.
Allah the Elevated said:
And I (Allah) created not the Jinn and mankind except that they worship Me (Alone). Adh Dhariyaat: 56
He also said:
And your Lord has decreed that you worship none but Him.Al Israa: 23
And verily, We have sent among every Ummah (community, nation) a Messenger (proclaiming): "Worship Allah (Alone), and avoid (or keep away from) Taghoot (all false deities, i.e. do not worship anything besides Allah)." An Nahl: 36
So all the messengers called to this creed, and all the divine Books were revealed clarifying it, clarifying what nullifies it, contradicts it and decreases it. All the creation who are accountable for worshiping Allah are ordered to believe in it. Since this is its status and importance, then it deserves special attention in researching and learning it before anything else, especially since the contentment of mankind is dependant on it, in the life of this world and the next; Allah said:
Whoever disbelieves in Taaghoot and believes in Allah, then he has grasped the most trustworthy handhold that will never break.Al Baqarah: 256
What this means, is that whoever this creed slips from, then indeed he is only holding on to delusion and falsehood, for what is it that remains after the truth except falsehood.
That is because Allah – He is the Truth (the only True God of all that exists, Who has no partners or rivals with Him), and what they (the polytheists) invoke besides Him, it is Baatil (falsehood).Al Hajj: 62
Furthermore, his destination would be the Fire, and what a wretched abode it is.
The meaning of ‘Aqeedah [creed] is: What one firmly believes in and considers as a part of his religion.
If this creed is in accordance to what Allah sent His messengers with, and revealed His Books with, then it is a sound and correct creed. With it one will be saved from Allah’s torment and would be content in the life of this world as well as the next.
If however this creed is in contradiction to what Allah sent His messengers with and revealed His Books with, then it is a creed that would necessitate torment for the person who holds it, as well as misery in the life of this world as well as the next.
فكل الرسل جاءوا بالدعوة إلى هذه العقيدة ، وكل الكتب الإلهية نزلت لبيانها وبيان ما يبطلها ويناقضها أو ينقصها ، وكل المكلفين من الخلق أمروا بها ، وإن ما كان هذا شأنه وأهميته لجدير بالعناية والبحث والتعرف عليه قبل كل شيء ، خصوصا وأن هذه العقيدة تتوقف عليها سعادة البشرية في الدنيا والآخرة .
فإن كانت هذه العقيدة موافقة لما بعث الله به رسله وأنزل به كتبه ؛ فهي عقيدة صحيحة سليمة ، تحصل بها النجاة من عذاب الله والسعادة في الدنيا والآخرة ، وإن كانت هذه العقيدة مخالفة لما أرسل الله به رسله وأنزل به كتبه ؛ فهي عقيدة توجب لأصحابها العذاب والشقاء في الدنيا والآخرة .