Jeremiah 1:9-10 recounts God's commission to Jeremiah, at the time a teenager.
Jeremiah's task was so important that God had prepared him for it from his conception (verse 5). He encouraged Jeremiah by telling him not to fear those to whom he would be sent, "for I am with you to deliver you" (verse 8). He ends His commission in verse 19, assuring Jeremiah that the people to whom he would be sent will "fight against you, but they shall not prevail against you. For I am with you, . . . to deliver you."
Jeremiah was destined to carry on God's work over the objections of entire nations and kingdoms (note the plurals). As Solomon writes in Ecclesiastes 3:2-3, God knows full well that there is "a time to plant, and a time to pluck what is planted; . . . a time to break down, and a time to build up." God did not only use Jeremiah in His purpose to root out, pull down, destroy, and overthrow the Perez-centered monarchy, but also to plant and build a Zerah-Perez monarchy.
Searching for Israel (Part Nine): The Migration of a Monarchy