The Prophet (peace be upon him and his household)’s most important responsibility was inviting people towards the truth and reality and striving on this path. He felt no anxiety in countering the dark world of his time. He was unafraid whether it was the period when he was alone in Makkah, or when he was surrounded by a small group of Muslims and faced with the arrogant Arab leaders, chiefs of Quraysh, and the rebels, with their harsh ethics and might, or when he was surrounded by the general population who had no cognition concerning his message. He spoke his message of truth, repeated it, explained it, clarified it, bore the insults, and the difficulties and pains until he was able to convert a large group of people to Islam. He was unafraid even on the day that he formed the Islamic government and took power as the head of that government.
Even during that time the Prophet was faced with different enemies and opponents; whether they were armed Arab groups – savage people who were scattered in the deserts of Hijaz and Yamama and Islam strove to reform them while they resisted – or whether they were the emperors of the time, i.e., Iran and Rome. He wrote letters to these empires, confronted them, had dialogues and discussions with them, fought against them, underwent many difficulties, and came under economic siege. The situation at this time became so bad that the people of Madinah would sometimes not have even bread to eat for two or three days. The Prophet was surrounded by many threats from all sides. Some people became worried, some wavered, some complained, and some encouraged the Prophet to compromise. However, in this setting of invitation and striving in the path of God (jihad), the Holy Prophet never weakened and took the Islamic society forward with strength and power until he elevated it to the height of its honor and power. It is that very system and society that was transformed into the world’s first power in the years to come through the blessing of the resistance of the Prophet in the battlefield and in his invitation.
Source: Ali Khamenei, The 250 Year Old Man