Disbelief...
Disbelief, like belief, has various degrees and ranks; and its effects also vary, like those of belief. TRADITIONS az-Zubayri says that he said to as-Sâdiq (a.s.): "Tell me how many ways of al-kufr ( = disbelief, infidelity, to cover) are there according to the Book of Allâh? Mighty and Great is He! He (the Imâm) said: `Disbelief, according to the Book of Allâh, is of five types.
There is the disbelief of denial (and denial is of two kinds), and the disbelief by neglecting what Allâh has ordered, and the disbelief of disavowal, and the ingratitude. As for the disbelief of denial, it is denial of the Lordship; it is the talk of those who say: "there is no Lord (i.e. Creator), nor any Garden nor Fire". It is the word of two groups of disbelievers who are called atheists. And they are those who say: "nothing destroys us but time" (45:24).
It is a religion invented by them as it seemed good to them, but they have no proof to support their view. That is why Allâh has said (about them): And they have no knowledge of that; they only conjecture (ibid.), that it is in reality as they say.
And He also said: Surely those who disbelieve, alike is it to them whether you warn them or do not warn them, they will not believe.' "(al-Kâfi) And as for the second kind, it is the denial after knowing; it means that the denier denies (the existence of God), but he knows (very well) that He is the truth, and he is convinced of it (in his heart). And Allâh has said (about such people): And they denied them unjustly and proudly while their soul had been convinced of them (27:14) ; . . .
and aforetime they used to pray for victory against those who disbelieved, but when there came to them that which they did recognize (i.e. the Prophet) they disbelieved in him; so Allâh's curse is on the unbelievers (2:89). So this is the explanation of the two kinds of denial.
And the third way of disbelief is ingratitude to the bounties (of Allâh) ; and it is as Allâh says quoting (the Prophet) Sulayman "This is of the grace of my Lord that He may try me whether I am grateful or ungrateful; and whoever is grateful, he is grateful only for his own self, and whoever is ungrateful, then surely my Lord is Self-sufficient, Honoured " (27:40) ; If you are grateful, I would certainly give you more, and if you are ungrateful, My chastisement is truly severe (14:7).
Therefore remember Me, I will remember you, and be thankful to Me, and do not be ungrateful to Me (2 :152) .