There are now many preachers. Not just religious. Many people are espousing and trying to convince the masses that they know what society should do.
How do we know who is right? Who should we believe?
The straightforward answer, as explained by Maimonides and by our sages throughout the ages, is that the revelation at Mount Sinai was an event witnessed by not just one or a few people (as is the case with other religions), but by millions of witnesses, from many different walks of life. They saw and heard the lightning and thunder, as G-d said, “I am the the Lord, your G-d, Who took you out of Egypt, from slavery.” And each generation relayed this experience to their children, right up to the present day.
At Mount Sinai G-d told Moses to tell all the nations of the world to adhere to the seven Noahide laws. Doing so will keep the world peaceful.
And the Jewish people were given the Torah, to study and to observe the laws therein.
So do you believe any smooth talking salesman? Or do you use common sense, trusting the historical occurrence that we, as a nation, saw with our own eyes.
Indeed, seeing is believing.