I as said before, greatness of the prophet is measured by his or her limitation to order their lives and words in strict accordance to the rhema word of God. Let us look at a few instances of this.
Num 22:18 And Balaam answered and said unto the servants of Balak, If Balak would give me his house full of silver and gold, I cannot go beyond ( pass over or cross over to the other side of; like crossing over a river ) the word ( Hebrew: the mouth) of the LORD my God, to do less or more.( to do the insignificant or what is great.)
20 And God came unto Balaam at night, and said unto him, If the men come to call thee, rise up, and go with them; but yet the word which I shall say unto thee, that shalt thou do.
35 And the angel of the LORD said unto Balaam, Go with the men: but only the word that I shall speak( Piel verb form ) unto thee, that thou shalt speak( Piel verb form). So Balaam went with the princes of Balak.
The prophet must speak forth in the accuracy of, the intent of God’s heart, and with the same degree of intensity of what the Lord Himself speaks.
38 And Balaam said unto Balak, Lo, I am come unto thee: have I now any power(dunamis) at all(dunamis) to say (intensive) anything? the word that God putteth in my mouth, that shall I speak ( intensive verb).
Hebrew: The only power that I have, is the power to speak the word of God. The word that God puts in my mouth I must speak as accurately and as emphatically as when God gave it to me.
Deuteronomy 4:2 Ye shall not add ( you shall not cause an addition or an exaggeration to what the Lord has spoken) unto the word which I command you, neither shall ye diminish(subtract, withdraw, or to hold back) ought from it, that ye may keep the commandments of the LORD your God which I command you.
Jer 23:28 The prophet that hath a dream, let him tell (recount, rehearse and declare the dream with the accuracy, the intention of God’s heart, as well same emphasis that God had in His telling of it. Hebrew emphatic verb)) a dream; and he that hath my word, let him speak (As accurately and thoroughly as God gave it to him or her; emphatic verb) my word faithfully (reliably and with certainty).