BismilLaahir Rahmaanir Raheem.
The reality of kufr and its various kinds is a lengthy topic, but we may sum it up in the following;
The importance of knowing what kufr is and the forms it may take:
The texts of the Qur’aan and Sunnah indicate that faith is not valid and is not accepted unless two conditions are met, which are what are implied by the testimony that there is none worthy of worship except Allah. These two conditions are submission to Allah alone (Tawheed), and denouncing and shunning all kinds of kufr and shirk. A person cannot denounce or shun anything unless he knows what it is. From this we understand the importance of knowing what Tawheed is, so that we may act accordingly and attain Tawheed, and knowing what kufr and shirk is so that we may avoid them and steer clear of them.
Kufr in Arabic means covering and concealing something.
In shar’ia terminology it means “not believing in Allah and His Messenger, whether that is accompanied by denial or it is not accompanied by denial but rather doubt, or turning away from faith out of jealousy or arrogance, or because one is following whims and desires that prevent one from following the message.
So kufr is the attribute of everyone who rejects something that Allah and His Messenger has commanded us to believe in, after news of that has reached him, whether he rejects it in his heart without uttering it, or he speaks those words of rejection without believing it in his heart, or he does both; or he does an action which is described in the texts as putting one beyond the pale of faith. See Majmoo’ al-Fataawa by Shaykh al-Islam Ibn Taymiyah, 12/335; al-Ihkaam fi Usool al-Ahkaam by Ibn Hazam, 1/45.
Ibn Hazam said in his book al-Fasl: “Rejecting something for which there is sound proof that there can be no faith without believing in it is kufr, and uttering words for which there is proof that uttering them is kufr is kufr. Doing any action for which there is proof that it is kufr is also kufr.”
To be continued in shaa Allaah. May Allah keep guiding us all and protect us from any satanic influences. Aameen.