How is He Mekadesh with Emunah?
Rashi: In the reward of the Emunah that in Galus, you believed in the promises via My Nevi'im.
Radak: It is a lasting Eirusin that will never falter.
Orchos Tzadikim (Sha'ar ha'Simchah DH Lachen Kol): The exiles will be gathered in the merit of Emunah.
Malbim: This corresponds to Mitzvos Bein Adam la'Makom. Their root is Emunah ? to believe in Hashem, His Torah and promises.
Why does it say "v'Yadata Es Hashem"?
Radak: "Ki Chulam Yed'u Osi lemi'Ktanam v'Ad Gedolam" (Yirmeyah 31:33).
Malbim: Corresponding to her bringing this gift of Emunah, He will bring a gift, that she will know Hashem. He will reveal to her signs, wonders and making the Shechinah dwell among them, to the point that they will have a clear knowledge of Hashem, like something sensed. Emunah will not be needed any more. Emunah is in something not known clearly, only it was received.
