Then I heard the voice of the Lord saying, "Whom shall I send, and who will go for us?" And I said, "Here am I; send me!" (Isaiah 6:8)
One of the great themes of science fiction and fantasy (and indeed, literature in general) is the hero's quest. Usually, the main character is an ordinary person who finds himself or herself called to complete a seemingly impossible task, but thanks to the help of many friends along the way and previously hidden reserves of inner strength, the task is accomplished and the proverbial day is saved.
Two of my favorite examples of questing heroes come from the pen of J.R.R. Tolkien: the hobbit Bilbo Baggins and his nephew Frodo. In The Hobbit, Bilbo is mistaken for a burglar and hired by a band of dwarves to help them steal back their treasure from Smaug the dragon. Frodo, whose story we read in the Lord of the Rings books, must carry the One Ring of power into the heart of it's evil creator's domain in order to destroy it and prevent Sauron's further domination. Although their neighbors might think both of them a little strange and remark upon their "Tookish" tendencies towards travel and adventures, each hobbit considers himself quite ordinary and quite unsuited for the important task placed upon his shoulders. However, each hobbit also agrees to go and attempt the quest despite much self-doubt and many misgivings.
Tolkien didn't come up with anything new here. In fact, the same theme occurs numerous times throughout the Bible. Moses makes excuse after excuse as to why he's not the right one to lead the enslaved Hebrew people out of Egypt. Isaiah declares himself to be "a man of unclean lips, and I live among a people of unclean lips" (Isaiah 6:5) when God asks him to deliver His messages - both of judgement and of hope - to the people of Judah. Jonah went so far as to run clear in the other direction when God asked him to take a warning message to the people of Ninevah. Ordinary people, with utterly human weaknesses, flaws, and failings, yet that's never the end of the story!
Bilbo, despite his bumbling, becomes the burglar that Gandalf knew he could be from the moment the "Burglar Lives Here" mark was made on the hobbit hole door. He helps the dwarves out of a number of scrapes and is instrumental in vanquishing the dragon and reclaiming the treasure. Assisted by both his friends and his enemies, Frodo manages to keep plodding along despite great weariness and danger until the One Ring is destroyed in the fires of Mount Doom, thus saving all of Middle Earth from certain destruction. God counters every one of Moses's arguments, appoints his brother Aaron to speak for him, and through him releases the Israelites from bondage. With a burning coal from the altar in the hands of a Seraph, Isaiah's unclean lips are purified and he steps forward to take God's message to His people. After enduring much trouble brought on by his own stubbornness, including 3 days in not-so-deluxe sub-marine accommodations, Jonah finally arrives in Ninevah and finds the people there receptive to God's message and willing to repent.
It doesn't stop there, either! Simon Peter, the bumbling fisherman whose ego writes checks that the rest of him can't cash, becomes one of the great leaders of the early Christian church. Saul, proud persecutor of Christians, does an about-face on the Damascus road and becomes the first great missionary in church history. I could go on and on....
All of these heroes have two things in common: they were all ordinary, imperfect people, and they all said "yes" to the call (however reluctantly). In addition, although they could have made excuses and refused the mission, they all trusted the call-er to know what he was doing and to have faith in their ability to do the job.
I am an ordinary person, but I too can do great things. All I have to do is say "yes" and trust the One who Calls to take care of the rest.