Jeremiah 1:19
And they shall fight against thee; but they shall not prevail against thee; for I am with thee, saith the LORD, to deliver thee. And they shall fight against thee; but they shall not prevail against thee; for I am with thee, saith the LORD, to deliver thee.
The promise was given to Jeremiah at his call to the prophetic office when he was still a youth, in the thirteenth year of the reign of Josiah. He belonged to the Levitical priesthood, had been trained from childhood for holy service, and had been set apart from birth to be a prophet to the nations. Yet at his call he felt unworthy and unable to speak, pleading that he was only a child. God looked upon him as one who had proved faithful in childhood and who would be true to his trust, standing for the right in the face of great opposition and enduring hardness as a good soldier. On that day God made him a fortified city, with an iron pillar and bronze walls, set against the whole land — against the kings of Judah and its princes and its priests and its people.
To him was pledged that all of them would fight against him but would not prevail over him. The work God commanded would not be defeated by opposition, because the Lord Himself would be with His messenger to deliver him. That assurance gives courage to continue in duty even when met with rejection and discouraging treatment.