Charles Ellicott Commentary Jeremiah 40:14

"and said unto him, Dost thou know that Baalis the king of the children of Ammon hath sent Ishmael the son of Nethaniah to take thy life? But Gedaliah the son of Ahikam believed them not." — Jeremiah 40:14 (ASV)

Do you certainly know that Baalis ... —The king of the Ammonites so named appears from Jeremiah 27:3 to have been in alliance with Zedekiah; and Ishmael, as belonging to the royal house of Judah, seems to have been still plotting with him against the authority of the Chaldeans. Open resistance now being impossible, they have recourse to assassination.

The plot becomes known, and Johanan, faithful to his new protector, warns Gedaliah against it, but, as the sequel shows, in vain. Gedaliah, in the guileless trustfulness of his character, does not believe that Ishmael is capable of such a crime and will not sanction another crime as a precaution.