O Messenger, deliver that which has been sent down to you from your Lord; for if you do not, you will have not performed His Messengership. God protects you against people; verily God will not guide the people of unbelief. (5:67)
The Messenger was sent to enlighten humanity about every dimension of human life. So, any neglect in delivering God's Message would amount to leaving humanity in darkness. For this reason, he continually sought unadulterated minds and hearts to which he could impart God's Message.
God's Messenger might have talked to people like Abu Bakr and 'Umar only a few times before they embraced Islam. But when it came to people like Abu Jahl, it was a different story. Each time he met them, he would say: "Proclaim there is no god but God and be saved." He would visit places where people gathered and make the same call. Occasional fairs were held in Makka and such nearby places as 'Arafat, Mina, Muzdalifah, and 'Aqabah—he would go to them every year, looking for receptive people.
When the Makkan polytheists' indifference was replaced with derision and mocking, and then with increasingly unbearable persecution, torture, and boycott, God's Messenger took Zayd ibn Haritha with him and went to Ta'if. But the people of this city also treated him harshly. The children lined up on either side of the road and threw stones at him. As he was wearing no armor, by the time he had left the town and found a tree under which to rest, he was bleeding profusely. He held up his hands and supplicated:
O God, unto You I complain of my frailty, lack of resources and significance before those people. O Most Merciful of the merciful, You are the Lord of the oppressed and are my Lord. To whom do You abandon me? To that stranger who looks askance and grimaces at me? Or to that enemy to whom You have given mastery over me? If Your indignation is not directed at me, I have no worry. But Your grace is much greater for me to wish for. I seek refuge in the light of Your Countenance, which illumines all darkness and by which the affairs of this life and the Hereafter have been rightly ordered, lest Your wrath alight upon me, or Your indignation descend upon me. I expect Your forgiveness until You are pleased. There is no resource or power but in You.
After saying this, he noticed that a tray had been placed before him. Addas, a Christian slave from Nineveh, had seen God's Messenger being stoned and tormented from the vineyard in which he was working. Putting some grapes on a tray, he had brought them to him. God's Messenger said "In the name of God" and began to eat. This surprised Addas, for it was the first time he had heard this phrase among the polytheists. So he asked God's Messenger who he was and why he had come to Ta'if. Upon hearing the answer, "I am Muhammad, from Makka, the Last Prophet," he said with tears in his eyes, Addas remarked: "God has made me find you," and embraced Islam. 
Prophet Muhammad was entirely focused on his mission. As a result, the circle of light broadened day by day, and the party of unbelief became more and more frustrated: They desire to extinguish with their mouths God's light; and God refuses but to perfect His light, though the unbelievers are averse (9:32). When no more could be accomplished in Makka, he emigrated to Madina and continued his mission there. Here he faced a different problem: established communities of hostile Jews and, eventually, a fifth column of Hypocrites who would ally themselves with his enemies.
In the twentythird year of his mission, he began to feel that his life was almost finished. He had performed the minor pilgrimage ('umrah) a few times, but never the major pilgrimage (hajj). He was able to do this during this final year. Ascending 'Arafat on the back of his camel, he preached what has become known as the Farewell Sermon. In it, he stressed that feuds and interest-based transactions were forbidden and that women have certain rights, and talked about family ties as well as tribal and national relationships.
A huge, tearful congregation listened to him. While speaking, he frequently asked them if he had communicated God's Message. With each positive reply, he raised his index finger toward Heaven and said: "O God, be witness!" In deep consciousness of Divine service, he might have thought: "God sent me to perform the duty of Messengership. Just as these people bore witness that I fulfilled this duty, I hope I may be regarded as having truly done it." He was prepared to meet God in perfect satisfaction.