The Characteristics of the True Believer
Al-'Allaamah 'Abdur-Rahmaan ibn Naasir As-Sa'dee
From the book: Essential Q&As about Eemaan (p.58-63)

[ In the Name of Allaah, the All-Merciful... ]

What are the characteristics of the believers that make them distinct from the disbelievers?

This is a great question indeed. By knowing the difference between the believers and other people, the difference between the Truth and falsehood becomes distinctly clear, as does the difference between the people of eternal happiness and the people of eternal misery.

Know that the true believer is the one who believes in Allaah and all of his Names and Attributes that are found in the Book and the Sunnah, upon their proper understandings. They must be fully acknowledged. Furthermore, the believer exalts Allaah, declaring Him free of anything that contradicts the perfection of His Names and Attributes. Thus, his heart becomes full of Eemaan, knowledge, conviction, serenity, and becomes totally concerned with Allaah.