Fundamentals Come First
“…It is a must to always strive to correct our fundamentals and principles and build our foundation on taqwa of Allah and His Pleasure. We were taught by our Prophet (صلى الله عليه و سلم) to begin with issues in order of their importance.
So, there is nothing before or above calling to pure monotheism and the firm handhold of faith (disassociation from false gods), and warning against and working to demolish the ideas of polytheism. This is how the Prophet was when calling the people, and this is what he would send his ambassadors and messengers with in all corners of the Earth, and this is what he would open his letters to the kings of the world with.
Therefore, we should not argue with deviant groups regarding their corruption in some secondary matters without tying it in to the fundamentals, as we know that this corruption only stems from the corruption in their fundamentals, namely in their understanding the concepts of polytheism, monotheism and its firm handhold, disbelief, faith, and other fundamentals.
In fact, we should start with nothing but their fundamentals that are deviated from those of Ahl as-Sunnah. So, if they correct their fundamentals and are sincere towards Allah and build their foundation upon taqwa of Allah and His Pleasure, it becomes easy to discuss these secondary matters with them, and it becomes possible to correct them…”