To be trusted and obeyed, the Messengers must be sinless and free from error and mistake; because people do not like to follow a person who is full of error, mistake and sin.
Everyone likes to follow and obey the people who have distinguished characteristics. A sinful person and the one who makes errors and mistakes could not be trusted and followed by the people. Since, the Messengers invite the people to the Divine religions; the people must trust them in order to accept their invitation. It is clear that the people cannot follow and trust the one who commit sins and mistakes. This is the main rationale behind the infallibility of the Messengers. In fact, gossips and accusations are the two main reasons that why the Messengers like David and Solomon, among others, suffered insults from the people and these insults are mentioned in the Bible. People are used to speak behind somebody’s back especially the prominent people like the Divine Apostles. They, also, like to spread it among themselves making a mountain out of a molehill. The Qur’an says: whoever obeys the Prophet (PBUH) has obeyed Allah (SWT). [1] Is it possible to be obedient to Allah by obeying someone who sins and makes mistake? [1] chapter 4, verse 80: مَنْ يطِعِ الرَّسُولَ فَقَدْ أَطَاعَ اللَّهَ وَمَنْ تَوَلَّى فَمَا أَرْسَلْنَاكَ عَلَيهِمْ حَفِيظًا