The Iron - 57:19 Those who believe in Allah and His messenger are the righteous and the martyrs. For them is a reward and light with their Lord. And those who disbelieve and deny Our verses are the inhabitants of Hell.
The most important criterion of belief:
The Cattle/6:82 Those who believe and do not mix their faith with wrongdoing, they deserve security and they have found the truth.

Luqman/31:13 "When Lokman advised his son, he said: "My dear son, do not associate partners with Allah; surely shirk (associating partners with God) is a great wrong."

The Companies/39:65 It has been revealed to you and those before you that if you associate partners, all that you do will be in vain and you will be of the losers.