Why does it say "Hineni" in this, the previous and the coming verses?
Radak (30): There were three divisions of false Nevi'im at the time. (a) Refer to 23:30:2:2. (b) There were Nevi'im who spoke clearly and eloquently - "ha'Lokchim Leshonam va'Yin'amu Ne'um". They promised Shalom to the nation in the name of Hashem, and supported their words through their eloquent speech, so people will heed them. About this it says 'one who prophesizes what was he did not hear [is Chayav Misah bi'Ydei Adam' - Sanhedrin 89a]. (c) Nevi'im of false dreams. They said that their dreams are Nevu'ah, and said them in Hashem's name.
What are "ha'Lokchim Leshonam va'Yin'amu Ne'um "?
Rashi: They train their tongues to say Sheker, and say 'Ne'um (so said) Hashem', like the true Nevi'im, in order that people will believe them.
Radak: They flatter. Also "Hitaso b'Rov Likchah b'Chelek Sefaseha Tadichenu" (Mishlei 7:21) means 'through her sweet lips (talk) she seduces him.'
Malbim: This refers to false Nevi'im who spoke in their own style. The only Sheker is the content. This is lighter than those who mimic the style of true Nevi'im (refer to 23:30:2:1).