http://revach.net/article.php?id=2527

Section: Parshas HaShavua   Category: Haftorah
Haftorah Matos/Three Weeks: Yirmiyahu Sees A Swift Stick and Hot Water
In the first Haftorah of the three weeks Hashem asks Yirmyahu, “What do you see?”  Yirmiyahu answers that he sees a stick made of an almond branch.  Hashem tells him that he is correct and tells him this symbolizes that the punishment will come swiftly.  After, Hashem asks again, and Yirmiyahu replies that he sees a boiling pot of water.  Here Hashem just goes straight to the explanation without congratulating him on his correct vision.  Why?

The Oheiv Yisroel (Likutim on Shemos) says that a stick can be many things.  It is a cane for support to an older person.  It is a staff of leadership to younger person.  It can also be a rod to punish people.  When Yirmiyahu correctly identified it, Hashem confirmed his answer. However a boiling pot obviously means trouble and needs no confirmation.

The Medrash says that from the time an almond tree sprouts until the fruit is ready is exactly 21 days.  These days represent the 21 days between Shiva Asar B’Tammuz and Tisha B’Av and the switness of Hashem’s judgment.