Jeremiah was only a teenager when he experienced God’s call on his life. Like Moses before him, he had lots of reasons to feel inadequate as we all do. He expressed his inadequacy to God in Jeremiah 1:6. He said, “Ah, Lord GOD! Behold, I do 
not know how to speak, for I am only a youth.” Isaiah also had several doubts about his calling. I wonder if J.R.R. Tolkien had these prophets in mind when he put similar hesitations in the dialogue of Frodo Baggins. I believe it was the wizard Gandalf that brought Frodo his calling regarding the one ring of great power. He was to take it to a certain distant mountain where he was to destroy it. Frodo answers, “I am not made for perilous quests.” He then adds. “I wish I had never seen the Ring! Why did it come to me? Why was I chosen?” Gandalf tells him, “Such questions cannot be answered.… You may be sure that it was not for any merit that others do not possess; not for power or wisdom, at any rate. But you have been chosen and you must therefore use such strength and heart and wits as you have.”
God promised to oversee Jeremiah’s ministry. One commentator says, “In Jeremiah’s call we see a splendid illustration of God’s attending providence which accompanies His purpose for our lives. Before God formed Jeremiah, He ‘knew’ him. Second, God ‘consecrated’ him, or set him apart. Third, God ‘appointed’ him. Before God formed Jeremiah, He defined His purpose for him and set him apart to do that work. Like all of us, Jeremiah struggled with a sense of inadequacy for his God-given assignment. He said, ‘I’m too young! I don’t know how to speak!’ But God rebuked him and clarified his thinking about his call. The important thing was not his age or his qualifications, but his calling. God’s calling of Jeremiah guaranteed that by God’s grace he would be adequate for the task. The Lord gave him two important instructions: first, don’t make excuses, and second, don’t fear. God made Jeremiah adequate for his calling by putting His words in his mouth, and His calling on his life. Where God guides, He provides!”
Two more commentators are worth noticing. One observes, “Jeremiah never gave up. He stood tall to the very end through a life of mostly failure. Our culture needs more Jeremiahs who sense their ordination in life and who pursue it. We have become an instant society, interested in short-term gains, immediate gratifications, and quick fixes. We have very little loyalty to the long term, perhaps because we have lost the sense of how far back our origins really do go.” Finally, the second writer says, “When Jeremiah was shown that the strength in which he was to act and speak was not his own and that he might always depend upon the Lord’s supply of grace and strength for his ministry, he no longer tried to avoid his call and commission. If we go in God’s strength we need not fear. Success for ministry does not depend on our ability but on His assistance.”