How can sorcerers begin to preach and speak about the Hereafter, God's punishment, and His reward immediately after believing, while they are new to faith?

What Moses (peace be upon him) called for, in terms of encouraging the afterlife and warning against Allah's punishment, was well-known, and he addressed the sorcerers with it. When they witnessed the miracle and realized the truth of his call, they articulated what he had been inviting them to: preferring what is with Allah, enduring in His obedience, holding firm to His monotheism, disregarding Pharaoh, and their faith so that Allah might forgive their sins. Thus, they were wicked sorcerers at the beginning of the day, and righteous martyrs by its end.