[22].Surah Al-Hajj [The Pilgrimage]: Ayat 17

Ayat 17. Verily, those who believe (in Allah and in His Messenger Muhammad [SAWW](PBUH), and those who are Jews, and the Sabians, and the Christians, and the Magians, and those who worship others besides Allah, truly, Allah will judge between them on the Day of Resurrection. Verily! Allah is Witness over all things.

[Tafseer] Those who believe (in the Quran´an), those who follow the Jewish (scriptures), and the Sabians, Christians, Magians, and Polytheists,- Allah will judge between them on the Day of Judgment: for Allah is witness of all things. In both those passages, the Muslims are mentioned with the Jews, Christians, and Sabians, as receiving Allah's protection and mercy. Here, besides the four religions, there is further mention of Magians and Polytheists: it is not said that they would receive Allah's Mercy, but only that Allah will judge between the various forms of faith. This is the only place where the Magians (Majus) are mentioned in the Qur'an. Their cult is a very ancient one. They consider Fire as the purest and noblest element, and worship it as a fit emblem of Allah. Their location was the Persian and Median uplands and the Mesopotamian valleys, their religion was reformed by Zardusht (date uncertain, about B.C. 600?). Their scripture is the Zend-Avesta, the bible of the ParsTs. They were "the Wise men of the East" mentioned in the Gospels. 
Hazrat Ubada bin As-Samit (May Allah be pleased with him) said: I, along with a group of people, gave the pledge of allegiance to The Messenger of Allah [SAWW](PBUH). He said, "I take your Pledge on the condition that you (1) will not join partners in worship with Allah, (2) will not steal, (3) will not commit illegal sexual intercourse, (4) will not kill your offspring (for fear of poverty), (5) will not slander, (6) and will not disobey me when I order you to do good. Whoever among you will abide by his pledge, his reward will be with Allah, and whoever commits any of those sins and receives the punishment in this world, that punishment will be an expiation for his sins and purification; but if Allah screens him, then it will be up to Allah to punish him if He will or excuse Him, if He will."

[Al-Bukhari Book 05, Chapter 58, Hadith # 232].

Lesson : as mentioned above in Surah Al-Hajj Ayat 17."and those who worship others besides Allah, truly, Allah will judge between them on the Day of Resurrection" This Hadith here the bring forth attention of muslim to their obligations, being fully conscious of their accountability to Allah (SWT) they are apt to make full efforts to provide justice and peace to other people. Shirk (polytheism) is an absolutely unpardonable sin. All other sins, how many and how grave they may be, can be forgiven by Allah. He will pardon them if He likes and send the sinful persons straight to Jannah, or keep them for a while in Hell and then shift them to Jannah. In any case, the punishment of Hell will not be eternal for them, as it is for the Mushriks (polytheist).