In the perspective of Shi‘ites, Verse 4: 64 of the Qur’an expresses an absolute order to follow the messengers, so they must be infallible. Verse 4: 59 and other such verses express the virtues of obedience and the terrible results of disobedience. Allah orders the servants to obey Him and His messengers, who are equivalent, according to verse 4: 80. So, if the prophet be not infallible, it is a contradictory order. In other verses, He orders: "Then do not obey the deniers" (68: 8), "And do not obey every worthless habitual swearer" (68: 10), "...do not obey from among them a sinner or ungrateful" ([http://tanzil.net/#trans/en.sahih/76:24 76: 24). So, the messengers are to be obeyed, the sinners are not to be obeyed, the result is that the messengers are not sinful.