On his own authority
"The one who speaks on his own authority seeks his own glory; but the one who seeks the glory of him who sent him is true, and in him there is no falsehood...When the Spirit of truth comes, he will guide you into all the truth, for he will not speak on his own authority, but whatever he hears he will speak, and he will declare to you the things that are to come". (John 7:18; 16:13, English Standard Version).
In these two verses there is a contrast regarding the same phrase in two different contexts. On both occasions, the Lord speaks; however, the first verse refers to a man, and the second verse refers to the Holy Spirit.
What kind of man is the one referred to in the first verse? It is someone who seeks his own glory; therefore, he speaks of himself, on his own authority. In the second verse, concerning the Holy Spirit, it is said: “He will not speak on his own authority, but whatever he hears he will speak.”
It is so easy for man to talk about himself in the spiritual things! He simply needs the right occasion and people willing to listen. However, these things are not circumstances necessarily prepared by the Lord.
To speak for God, one must have heard God first. That is why the spirit says, “But whatever he hears, he will speak”. To hear God is not a matter of a couple of minutes. It is not simply a matter of opening the Bible and having God speak to us, teaching us, and sending us with a message. To hear God requires taking all the time He deems necessary (Is. 50:4-5), purifying the heart (Jas. 4:8), and waiting on His mercy. God has no obligation to give us a word to speak to His people. He can use another vessel that is cleaner, or He might simply not want to speak that day.
In Jeremiah, God has very strong complaints against the lying prophets who are saying what God never ordered them to say: “Thus says the Lord of hosts: Do not listen to the words of the prophets who prophesy to you. They make you worthless; they speak a vision of their own heart, not from the mouth of the Lord. They continually say to those who despise Me, ‘The Lord has said, “You shall have peace”’, and to everyone who walks according to the dictates of his own heart, they say ‘No evil shall come upon you.’” For who has stood in the counsel of the Lord, and has perceived and heard His word? Who has marked His word and heard it? ... I have not sent these prophets, yet they ran. I have not spoken to them, yet they prophesied. But if they had stood in My counsel, and had caused My people to hear My words, then they would have turned them from their evil way and from the evil of their doings… Therefore behold, I am against those who prophesy false dreams, and tell them, and cause My people to err by their lies and by their recklessness. Yet I did not send them or command them; therefore, they shall not profit this people at all, says the Lord” (Jeremiah 23:16-2, New King James Version).
Do you know prophets of this kind? Probably more than one. Pay attention to their message, and you will notice that they err. They speak from their own heart; God never sent them. The gospel they preach aims to build a kingdom in this world. They seek their own glory. On the other hand, when someone speaks by the Holy Spirit, he will seek to glorify only Jesus Christ the Lord.