Allah covers humans with three types of coats. The first coat is human’s clothes that conceal his/her unpleasant and shameful parts. The second one is the concealment of his ideas, thoughts and dreams in his heart. The third one is that Allah has covered and concealed his creatures’ sins, turned his sins into merits, given to man his book in which only his good deeds are written in afterlife as if he has not committed any sins. (Ghazali, Asmau'l-Husna, trnsl. by Y. Arıkan, p. 128) 20.47
Accordingly, the sins that lie snug in this world also lie snug in afterlife. The sins committed publicly are seen in afterlife publicly, too.
Allah is not going to show all sins to everyone. Thus, Allah is going to conceal some of the sins that are repented and the sins of those who conceal others’ sins.
Allah’s creatures are not just the man. As a matter of fact, man’s good deeds and bad deeds are going to be shown to the whole universe, to angels and to many beings.
Above all, by this way, Allah will have shown and declared his justice and that He gives everyone what he deserves. First of all, Allah will show this to the person himself.
“Even if a person who commits sodomy washes himself with water of seas cannot clear up his sin. Only repent clears it up.” (Daylami, Firdawsu’l-Akhbar, No: 6892; Ajluni, Kashfu’l-Khafa, No: 2093)
The narrative above lets us know that a sincere repentance before death will cause the sins to be forgiven.
Accordingly, the sins that will not be forgiven -no matter whether they are committed publicly or secretly- can be interpreted as the ones that are not repented.