It has just been explained that the belief of Sunni'ism regarding the Constitution of Caliphate weakened the Muslims politically; and made them obey anyone who succeeded in hig bid of power irrespective of his qualifications and character.
As though it was not enough, it cornpelled them to change their total religions outlook and beliefs. First of all, an overwhelming majority of their Caliphs was devoid of any sense of religious propriety and piety. Now, to justify thc Caliphate of such Caliphs they had to say that even the prophets used to commit sins. Thus, the belief in the 'Ismat' (Sinlessness) of the Prophets was changed.
Again, as almost always there were hundreds of people more knowledgeable, morc pious and more qualified for the Caliphate than the Caliph on the throne, they had to say that "there is nothing wrong in giving preference to an inferior person over a superior person."
But it was pointed out by the Shias that it is 'evil' according to the sReason' to give preference to an inferior when a superior person is available. In reply the Sunnis had to declare that there is nothing good or evil in itself; whatever God tells us to do becomes good; whatever He forbids, becomes evil.
And as for the 'Reason' they denied it any place in the Religion. It,is not possible to go in further details to show how the belief in Sunm's Constitution of Caliphate effected the whole fabric of Islamic theology. But I think this short explanation will be cnough at present.
From this, it will appear that not only the prophets were deprived of their 'Ismat' but even God was deprived of His 'Justice.' In this background, it is easy to understand the full significance of the Ayat which was revealed at Ghadeer:
"O Apostlej proclaim what hath been sent down to thee from they Lord (i.e. Caliphate of Ali); and if thou doth it not, then thou did r.ot proclaim His message (at all): and God will protect thee from (evil) men."
As the purity of Islamic belief and deeds depended upon the Caliphate of Ali(as), it was said that if that one message was not proclaimed then it will mean that no message was proclaimed at all; because the safety of the whole religion depended upon Ali being the Caliph after The Holy Prophet.