Then you also agree with the need of knowing those who do not err!
And it also originates the need to know & keep in mind those who err in past so that we may not follow their footprints unknowingly.
And there has to be some protected ones who are protected by Allah & who do not err.
Allah says in 20:115 that Adam did not have the same level of determination as the Messengers of 42:13. The ulul `azm messengers (possessors of determination) were Muhammad (s), Noah, Abraham, Moses, and Jesus. Each of them were given a scripture and a system of law that abrogated and replaced what came before it.
The moment you understand that Allah سُبْحَانَهُ وَ تَعَالَى creates and choose whatever He wish, the moment you understand that He give ranks to whomever He will greater than to others, and Exalted is He who choose whatever He wish and whatever He choose is nothing but Goodness and Amazement of His greatness.