Kriteria untuk menilai sama ada seorang Muslim memiliki Syakhsiyyah Islamiyyah ialah kesahihan akidah Islamnya serta pembinaan pemikiran dan kecenderungannya di atas akidah tersebut. Selagi asasnya sahih dan pembinaan pemikiran serta kecenderungannya hanya berdasarkan akidah Islam, kesilapan tidak sengaja yang jarang berlaku, iaitu kekurangan dalam tingkah laku, tidak menjejaskan syakhsiyyah Islamiyyah seorang Muslim. Tetapi jika akidah itu rosak, maka orang tersebut terkeluar daripada Islam, walaupun amalannya dibina atas hukum-hukum Islam, kerana dalam keadaan itu amalannya tidak dibina atas keyakinan yang kukuh [i'tiqad], sebaliknya atas sesuatu selain keyakinan yang kukuh: sama ada atas kebiasaan atau adat, atas menurut orang ramai, atas manfaat (yang disangka) daripada amalan tersebut, atau atas selain itu. Jika proses pembinaan itu rosak kerana menjadikan manfaat atau akal sebagai asas untuk membina tingkah laku, orang itu tetap seorang Muslim kerana akidahnya sahih, tetapi dia bukan syakhsiyyah Islamiyyah, walaupun dia termasuk dalam kalangan pembawa Da'wah Islam, dan walaupun seluruh tingkah lakunya selaras dengan hukum-hukum Islam. Ini kerana yang menjadikan seseorang itu syakhsiyyah Islamiyyah ialah pembinaan pemikiran dan kecenderungannya di atas akidah Islam disebabkan keimanan kepadanya. Oleh itu, wajib bagi mereka yang mencintai Islam dan mahu ia berkuasa serta menang, tetapi tidak membina pemikiran mereka di atas pemikiran dan hukum-hukumnya, melainkan di atas fikiran, kepentingan atau keinginan mereka sendiri, untuk berhati-hati terhadap perbuatan seperti ini, kerana ia menjauhkan mereka daripada menjadi syakhsiyyah Islamiyyah; sekalipun akidah mereka utuh dan sekalipun mereka sangat berilmu tentang pemikiran dan hukum-hukum Islam. Antara perkara yang wajib diberi perhatian ialah bahawa menganut akidah Islam bermakna beriman kepada segala yang dibawa oleh Rasulullah ﷺ, secara keseluruhan, dan kepada apa yang ditetapkan dengan dalil yang qat'i, serta menerima kesemua ini dengan reda dan berserah diri. Perlu diketahui bahawa sekadar mengetahuan tidak mencukupi, dan menolak walaupun perkara yang paling kecil yang telah terbukti secara qat'i sebagai sebahagian daripada Islam mengeluarkan seseorang itu dan memutuskannya daripada akidah. Islam ialah satu kesatuan yang tidak boleh dipisah-pisahkan dari segi iman dan penerimaan; meninggalkan (walaupun) sebahagian daripadanya membawa kepada kufur. Oleh itu, kepercayaan bahawa agama dipisahkan daripada kehidupan atau daripada Negara ialah kufur yang tidak dapat dipertikaikan. Allah سُبْحَانَهُۥ وَتَعَالَىٰ berfirman,
The criterion for judging whether a Muslim holds an Islamic Shaksiyyah is the soundness of his Islamic ‘aqīdah (creed) and the building of his thoughts and inclinations upon it. As long as the basis is sound and the building of thought and inclinations are exclusively on the Islamic ‘aqīdah (creed), rare inadvertent errors, that is, gaps in conduct do not compromise a Muslim’s Islamic shakhsiyya (personality). But if the ‘aqīdah (creed) becomes flawed, this removes the person from Islam, even if his deeds are built on the ahkām (rules) of Islam, because in that case they would not be built on firm conviction [i’tiqād] but on other than firm conviction: either on habit or custom, on conformity to people, on the (perceived) benefit of such deeds or on other than that. If the building process becomes flawed due to the use of benefit or the intellect as the basis on which to build behaviour, the person would be a Muslim due to the soundness of his ‘aqīdah (creed), but he would not be an Islamic shakhsiyya (personality), even if he was among the carriers of the Islamic Da’wah, even if all his conduct is in conformity to the ahkām (rules) of Islam. This is because what makes one an Islamic personality is the building of thought and inclinations on the Islamic ‘aqīdah due to belief in it. To this end, it is imperative for those who love Islam and want it to be dominant and victorious but do not build their thinking on its thoughts and rules but rather on their own minds, interests or desires, to be wary of such a deed, because it distances them from being Islamic personalities; even if their ‘aqīdah (creed) is intact and even if they were highly knowledgeable of the thoughts and ahkām (rules) of Islam. Of that which is imperative to draw attention to is the fact that embracing the Islamic ‘aqīdah (creed) means belief in all that the Messenger ﷺ came with, as a whole, and in that which is established by definitive [qat’i] evidence, and that the acceptance of all this be accepted with contentment and submission. It should be known that mere knowledge does not suffice and that rejecting even the most minor of matters proven definitively as part of Islam removes the person, and detaches him, from the ‘aqīdah (creed). Islam is an indivisible whole as fair as belief and acceptance is concerned; relinquishment of (even) a part of it is entails disbelief [kufr]. Hence the belief in the separation of the deen from life or from the State is indisputable kuf (disbelief). Allah الله سُبْحَانَهُۥ وَتَعَالَىٰ says,