He admits Nehemiah, and seems, as he does so, to be in a great state of fear and terror.
Then he whispers a dreadful secret in his ear.

He tells Nehemiah that his life is in immediate danger, that there is a plot set on foot by Sanballat to murder him that very night, and that this plot has been revealed to him by God.

He tells him that he feels his own life, as one of Nehemiah's best friends, is also in danger, and therefore he proposes that they shall go together after dark to the temple courts, and, passing through these, enter into the sanctuary itself, the Holy Place, in which stood the altar of incense, the golden candlestick, and the table of showbread.

There, having carefully closed the folding doors of fir-wood, they may hide till daybreak, and those who were coming to assassinate Nehemiah will seek him in vain.
Shemaiah gives this advice as a direct message from God, but Nehemiah saw through it.

He felt sure God could not have sent that message, for God cannot contradict His own Word.