How Do We Purify our Hearts From Doubts and Shirk

It is obligatory upon a person to correct his intention, rectify his heart,and look at the doubt in his heart and remove this doubt (i.e., and change it) to certainty,How? If a person has doubt, how can it become Yaqeen (certainty)?He should look at the Ayat "Indeed, in the creation of the heavens and the earth and the alternation of the night and day are signs for people of understanding." [Āl-Imran:190], "And in the creation of yourselves and what He disperses of moving creatures are signs for people who are certain [in faith]." [Al-Jathiyah:4] So, look at the Ayat of Allah if the Shaytan casts doubt into your heart. So, look at the Ayat of Allah, look at this universe, who manages it? See how do the conditions change, how Allah alternates the days among people until you know that this universe has a Wise Disposer of affairs, Exalted is He. Purify your heart from Shirk (disbelief). How do I purify my heart from Shirk? I purify my heart by telling myself that people won’t benefit me. If I disobey Allah, they will not save me from the punishment. And if I obey Allah, they won't reward me. Who brings you the reward? It is Allah. Who saves you from the punishment? It is Allah. If it's so, then why do you commit Shirk (polytheism / disbelief) with Allah the Almighty? Why do you intend by your worship to get closer to the creation (i.e., rather than the Creator)?! Always be in a state of purifying your heart until it is purified, as Allah said, "Those are the ones for whom Allah does not intend to purify their hearts" [Al-Ma'idah 41] Allah does not intend to purify their hearts. So, purifying the heart is a very important matter. I ask Allah to purify my heart and your hearts, and make us sincere to Him and followers of His Messenger ﷺ.