Final answer:
Faustus begins to believe that human salvation is impossible because he makes a pact with the devil, loses faith in God, and deems his sins unforgivable.
Step-by-step explanation:
In Christopher Marlowe's "The Tragical History of Doctor Faustus," Faustus begins to believe that human salvation is impossible because he makes a pact with the devil. According to the legend, Faustus, a bored scholar, trades his soul to gain worldly pleasures, such as power and knowledge, from the devil. This pact leads Faustus to lose faith in God and believe that his actions and sins are unforgivable, ultimately resulting in his despair and belief in the impossibility of salvation.