The third condition to obtaining forgiveness is Tawheed and it is the greatest condition. Whoever lacks Tawheed will not obtain forgiveness, and whoever comes to Allah with Tawheed has come with the greatest means of earning His forgiveness. Allah says:
Indeed, Allah does not forgive that others should be worshipped along with Him (shirk), but He forgives whatever is less than that to whom He wills.
[Soorah An-Nisaa, 4:48]
Whoever comes with Tawheed and as much as the earth full of sins, Allah will meet him with as much forgiveness. However, it must be known that this is Allah’s decision; if He wills, He may forgive him, or He may take him to account for his sins. However, the result is that such a person (who has actualized and died upon Tawheed) will not reside forever in the Fire. Rather, he will be taken out and allowed to enter Paradise.
Some scholars have said that the one who actualizes Tawheed will not even be thrown into the Fire as the disbelievers will, nor will he reside therein as disbelievers will. So if the Tawheed of a servant is complete and he is sincere to Allah in it and fulfills all its conditions with his heart, tongue, and limbs, or with his heart and tongue at the time of his death, then that would necessitate for him complete forgiveness for whatever previous sins he may have committed. It would also prevent him from entering the Fire. So whoever actualizes Tawheed with his heart completely empty of everything but Allah out of love, honor, respect, fear, hope, and reliance; then that would remove his sins and misdeeds even if they were as much as the foam of the sea. Perhaps they would even be exchanged for good deeds in their place as has been mentioned in the narrations of bad deeds being replaced with good ones. Undeniably, this Tawheed is the greatest of all cures. Even in its most basic form, were it to be joined with a mountain of sins and bad deeds, it would surely replace them all with good deeds.