So what I think you are asking is on what grounds or authority did they have to preach. Jesus said who sent the son of man. All the prophets of the Lord have said they speak what the Lord told them. Here is a sample;
Quote:Thus says the Lord of hosts:)
Seek the Lord, all you humble of the earth, who have observed his law; Seek justice, seek humility; perhaps you may be sheltered on the day of the Lord’s anger.
I will change and purify the lips of the peoples, That they may all call upon the name of the Lord, to serve him with one accord;
Render true judgment, and show kindness and compassion toward each other.
They shall call upon my name, and I will hear them. I will say, "They are my people," and they shall say, "The Lord is my God."
I am the bread of life; whoever comes to me will never hunger, and whoever believes in me will never thirst.
Everything that the Lord gives me will come to me, and I will not reject anyone who comes to me, because I came down from heaven not to do my own will but the will of the one who sent me.
My teaching is not my own it comes from the one who sent me.
Whoever chooses to do his will shall know about this teaching namely, whether it comes from God or whether I‘m speaking on my own.
Whoever speaks on his own seeks his own glory, but whoever seeks the glory of the one who sent him is truthful, and there is no dishonesty in his heart.
I came into the world as light, so that everyone who believes in me might not remain in darkness. And if anyone hears my words and does not keep them, I do not condemn him, for I did not come to condemn the world but to save it.
Whoever rejects me and does not accept my words he already has his judge, namely, the word that I have spoken that’s what will condemn him on the last day, because I did not speak on my own, but the Lord who sent me commanded me what to say and how to speak, and since I know that his commandment means eternal life what I say is spoken just as He instructed me."