Why did Allah make Christians believe in the crucifixion and death of the Messiah as a result of sensory observation, when that is not the truth, and how can they be convinced of the opposite of what they witnessed?

Allah did not declare the early Christians disbelievers because they believed that Christ was killed and crucified, but rather because of their disbelief in making Christ a god and making the gods three. The error in believing in the crucifixion was excusable before the advent of Prophet Muhammad and the revelation of the Qur’an, which definitively negated it. So, whoever believes in it after the revelation of the Qur’an is a disbeliever, for he has denied the news of Allah.

The Qur’an indicates that the Jews were deluded, and they were unable to kill Christ or crucify him; rather, Allah raised him to Himself.

A Muslim invites a Christian to Islam and to believe in the oneness of Allah and the prophethood of Muhammad, peace be upon him. Thereupon, it becomes easy for him to accept the Qur’an's negation of Christ's crucifixion, and that the historical incident of the crucifixion is questionable, with nothing to confirm it through continuous transmission (Tawatur).