"'O Jacob My servant, do not fear,' declares the Lord,
'For I am with you. For I will make a full end of all the nations
Where I have driven you,
Yet I will not make a full end of you;
But I will correct you properly
And by no means leave you unpunished."' Jeremiah 46:28 (NAS)
God allowed His people to be punished for their disobedience by other nations, but He also promised to punish the nations who punished His people.
"Now so that your heart does not grow faint,
And you are not afraid at the report that will be heard in the land--
For the report will come one year,
And after that another report in another year,
And violence will be in the land
With ruler against ruler--
Therefore behold, days are coming
When I will punish the idols of Babylon;
And her whole land will be put to shame." Jeremiah 51:46-47 (NAS)
God can't overlook evil, and it will always be punished in the end. He will remember wrongs that have been done to you, and He will avenge. Be on His side, and do what's right, and you won't have to be afraid.
"You drew near when I called on You;
You said, 'Do not fear.'" Lamentations 3:57 (NAS)
Pray. He'll hear you.
"Like emery harder than flint I have made your forehead. Do not be afraid of them or be dismayed before them, though they are a rebellious house." Ezekiel 3:9 (NAS)
God sent Ezekiel to deliver a message to hardheaded people who He already knew wouldn't listen to it. He made Ezekiel just as headstrong as the rebels to whom he was sent. Do the job you're commissioned to do, whether you feel successful or not.
"Then he said to me, 'Do not be afraid Daniel, for from the first day that you set your heart on understanding this and on humbling yourself before your God, your words were heard, and I have come in response to your words.'" Daniel 10:12 (NAS)
This was an angel sent to minister to Daniel. Set your own heart on understanding what the Lord has to tell you and humbling yourself before God, speak the words He gives you, and angels will be released to aid you as well.