The Three Principles (Al Usool Ath Thalaathah) by Muhammad ibn Abdil Wahhaab, coveres the three questions we will be asked in our graves once we die:
“WHO IS YOUR LORD? WHAT IS YOUR RELIGION? WHO IS YOUR PROPHET?”
Shaykh Saalih al Fawzaan said in his explanation of the book:
"So before us is this treatise – the treatise “The Three Fundamental Principles” – and it is a tremendous treatise which is brief, supported by evidences from the Book of Allaah and the Sunnah of his Messenger sall Allaahu ‘alaihi wa sallam.
And this small treatise is about a tremendous fundamental matter from the fundamentals of Islaam, and it is ‘aqeedah – creed and belief. And the scholars give importance to these brief works, authoring them and exerting themselves in keeping them brief and refining them; then they would encourage their students to memorise them so that they should remain fundamental assets for them and a store of provision for them from which they can derive benefit, and through which they bring benefit to others.
And beginning with these shorter works is the foundation for the students of knowledge, so the student of knowledge should begin by learning little by little, taking from the initial points of knowledge and its fundamentals and then proceeding in stages through it."
If you are looking to study Al Usool Ath Thalaathah, these resources may be helpful:
1. AUDIO LESSONS on the Three Principles by Abu Talhah Dawood Burbank onwww.ittibaa.com. Basically, it is a verbatim translation of Shaykh Saalih al Fawzaan’s explantion of the book that you can listen to with quotes from other scholars also included. About fifty lessons each lasting an hour at most.
2. The THREE PRINCIPLES Multiple Choice Questions (MCQs) by Abu Abdirrahmaan Nasser ibn Najam to accompany the audio lessons, although you can use then as a stand-alone learning aid. Checked by Abu Talhah. Although 400 pages long, they are not as daunting as they look. Much of the document consists of translations from the scholars in addition to the simple MCQs. Multiple choice tests not just what you know for sure but also identifies if you know why something is not true. That means these questions are not as easy as they look… A tried and tested resource popular with many we know.