From Fr. Jude Botelho:
The great prophets were directly called by God and sent to bear witness to the people. The fact that they were sent by God constituted their mission. In today's reading we hear of Jeremiah's vocation to be a prophet. The Lord tells him that he was chosen for the task even before he was born, that he was consecrated in his mother's womb. The calling of a prophet was not an easy task. A prophet was never popular and he had to speak the plain and difficult truth and say harsh things that needed to be said. Their message would be rejected and so would they, but God would be on their side and He would be their support. Jeremiah, like any true prophet, was rejected by the people but he carried on.