"'Today I have made you a fortified city, an iron pillar and a bronze wall to stand against the whole land - against the kings of Judah, its officials, its priests and the people of the land.'" NIV translation
God informs Jeremiah that everyone from every class of society was going to be against him but He also reminds the prophet that God is the source of his strength. This is a good lesson for us as well in that, sometimes, it may seem like we are standing alone in faith and following what God asks us to do but really God is with us and in us to give us the strength.
"'They will fight against you but will not overcome you, for I am with you and will rescue you,' declares the Lord." NIV translation
A gambler would not have liked the odds here as Jeremiah was told that it was going to be everyone against him. But, God also declared that he was on the prophet's side and that changes things dramatically. We, too, can take comfort in the fact that it does not matter how many oppose us if God is with us.