1)
What tense is "Yachres"?
1.
Radak #1: It is future (this is a Nevu'ah).
2.
Radak #2: It is a command (this is a Tefilah).
2)
What is "Lashon Medaberes Gedolos"?
1.
Radak: It speaks Dibros Gedolos or Gevohos (great or haughty matters). This is like "k'Eder ha'Ketzuvos" (Shir ha'Shirim 4:2; it should say 'k'Eder Rechelim ha'Ketzuvos'), "Ma'achalo Beri'ah" (Chabakuk 1:16; 'Seh' is omitted) and similar verses.
2.
Malbim: It is haughty matters in matters of Emunah. Lashon refers to matters of understanding; they falsify Emunah and deny [Torah] creed.