Here is a very interesting book on the fundamentals of Islamic belief. Its author wrote it in response to the question: "What will the servant be questioned on the day of judgment?
Abdulaziz Ibn Marzuq At-Tarifi
No one may interpret Islam and how God wants it to be except God Himself, in his book, the Qur’an, and in the Sunnah of the Prophet. No human being has a higher status than God’s Prophet, yet he only delivers what God reveals to him.
Taken together, words, action and belief constitute faith. Maghrib prayer consists of three rak[ahs and if one is not included, the prayer is not Maghrib. By the same token if any of the three elements: words, action and belief is lacking, the condition is not called faith.
The Qur’an is God’s word: He truly said it in sounds, words and surahs. We do not say that ‘it is mere meaning without utterance’, but we say that God speaks whenever He wills: ‘God has spoken His word directly to Moses’. (4: 164).
When revealed text and rational thinking are combined together, religious truth is fully understood. Revealed text is of no benefit to one who has no reason, and reason on its own is of no help to one who has no knowledge of revelation.
Death is inevitable. God says: ‘All that lives on it perishes; but forever will remain the face of your Lord, full of majesty, granting grace’. (55: 26–7) It is a part of faith that we should believe in what comes after death, including one’s examination in the grave and the resulting happiness or torment.
To stay with the community is obligatory and no community exists without a leader, or imam. The leader of the Muslim community is obeyed in line with the obedience of God, who says: ‘Believers, obey God and obey the messenger and those from among you who have been entrusted with authority’. (4: 59)
Jihad continues until the end of human life and remains in force all of the time, as long as the Qur’an remains. In an authentic hadith, Jabir reports that the Prophet said: ‘A group of my community will continue to fight for the truth, prevailing until the Day of Judgement’.
The best of people are prophets, then Prophet Muhammad’s companions. Their high status is stated in the Qur’an: ‘Muhammad is God’s Messenger; and those who are with him are firm and unyielding towards the unbelievers, full of mercy towards one another. You can see them bowing down, prostrating in prayer, seeking favour with God and His good pleasure’. (48: 29)