It's because Moses is the only one who demonstrated his credibility to the entire nation. Without that, I'd have no reason to ever believe anyone claiming to be a prophet.........
There's no reason to take the word of a person claiming to be a prophet of G-d on their say so, because their signs could be reasoned away. But at Mt. Sinai, the entire nation experienced a clear revelation of G-d with Moses. That established his prophetic nature beyond any doubt.
But all you have is scriptures saying that the entire nation experienced a clear revelation of God with Moses.There are no eyewitnesses alive today so there is no way to
verify that ever happened as recorded in the scriptures.As I am sure you know, there are various interpretations of the scripture regarding
what actually happened on Mt. Sinai. How can an outsider like me know what actually happened? I was just reading on this website:
What Really Happened at Mount Sinai? - TheTorah.com
What do you think actually happened to the nation on Mt. Sinai? How exactly did the Israelites experience God?
Regarding what happened to the Israelites on Mt. Sinai, I cannot say if there is an authoritative Baha’i position, but there is an authoritative Baha’i position regarding what happened to Moses on Mt. Sinai, that God spoke to Moses at the Burning Bush, because it is recorded in the Writings of Baha’u’llah.
“He went forth from the city, and sojourned in Midian in the service of Shoeb. While returning, Moses entered the holy vale, situate in the wilderness of Sinai, and there beheld the vision of the King of glory from the “Tree that belongeth neither to the East nor to the West.” 19 There He heard the soul-stirring Voice of the Spirit speaking from out of the kindled Fire, bidding Him to shed upon Pharaonic souls the light of divine guidance; so that, liberating them from the shadows of the valley of self and desire, He might enable them to attain the meads of heavenly delight, and delivering them, through the Salsabíl of renunciation, from the bewilderment of remoteness, cause them to enter the peaceful city of the divine presence.” The Kitáb-i-Íqán, pp. 54-55
Christians and Muslims and Baha’is
also have scriptures saying that their Prophets heard the Voice of God. How is what you have for Moses any different from what we have? I am just trying to use logic here and reason.
So basically, every other prophet relies on the commandment in the Torah that Moses prophesied to obey a prophet who passes the tests establishing his prophecy (without which, we'd have no strong reason to believe them). Since they're authority only comes through Moses' prophecy, they don't have the wherewithal to contradict him.
I do not have a problem with Moses' prophecy to obey a prophet who passes the tests establishing his prophecy. From a Baha’i point of view, to contradict Moses one would be contradicting God, since we believe that Moses was a Prophet of God whose Will was identical with the Will of God...
Deuteronomy 18:22 When a prophet speaketh in the name of the Lord, if the thing follow not, nor come to pass, that is the thing which the Lord hath not spoken, but the prophet hath spoken it presumptuously: thou shalt not be afraid of him.