To answer best this question, let's first consider who Muhammad was and who he claimed to be, Muhammad claimed to be a prophet in the likes of, and in succession to, Moses and Jesus. However, and more importantly, he claimed to be a messenger, and apostle, bring a new revelation, a new message from God, and a commission to establish anew the pure religion of God to mankind. As an apostle, he demanded strict and absolute obedience and fealty to himself and his message, but should we accept his claim of being a divine messenger from God?
Historically, the apostles and messengers who brought with them a new message and a new religion from God did so with signs and wonders to validate and succor their claim of their divine mission. Moses performed many miracles before Pharaoh and the Israelites. Jesus also performed miracles, even the raising of the dead, for which He challenged the people, "If I do not do the works of My Father, do not believe Me; but if I do them, though you do not believe Me, believe the works, so that you may know and understand that the Father is in Me, and I in the Father." (John 10:37-38) Finally, the Apostles of Jesus also demonstrated the reality of their message with signs and wonders of which it was written, "After it was at the first spoken through the Lord, it was confirmed to us by those who heard, God also testifying with them, both by signs and wonders and by various miracles and by gifts of the Holy Spirit according to His own will." (Hebrews 2:3-4) However, Muhammad gives us no miracles, no signs and wonders, no evidence of his apostleship other than his own word, nor is there anyone who can corroborate that God actually spoke to Muhammad as those did who heard God speak to Jesus. "So the crowd of people who stood by and heard it were saying that it had thundered; others were saying, 'An angel has spoken to Him.' Jesus answered and said, 'This voice has not come for My sake, but for your sakes.'" (John 12:29-30)
Similarly, we must consider the nature of Muhammad including his morality and inclination for war. Muhammad was a man of an intense sexual appetite. He has fourteen wives including an unspecified number of concubine and slaves at his disposal, including one wife who was only nine when he married her. While Muhammad was not the first to have multiple wives, he was the first to use his prophetic claims to justify his many wives and to rebuke the jealousy of one wife who complained against his preference for another. He was also the first in the Abrahamic stream to claim a direct word of God justifying and pronouncing polygamy both normal, permitted, and divinely inspired. How different is Muhammad's idea of marriage from that of the first marriage instituted by God. "God created man in His own image, in the image of God He created him; male and female He created them. God blessed them; and God said to them, 'Be fruitful and multiply, and fill the earth'" (Genesis 1:27-28)
Muhammad, while starting out as a reformer, ended up being a man of war, a man of conquest, and the sheder of much blood. His method of evangelism and the conversion of the infidels was through force, compulsion, and open war. Again, Islam is not the only religion to resort to force to convert the unbelievers, but it is unique among other Abrahamic religion to claim God's sanction on such methods. While Israel did use warfare to claim their inheritance from God, they claimed no commission from God to concur the world and the surrounding nations to the faith of their God and to force them into compliance to their religion and laws. How different was Muhammad's motives and methods to those of Jesus when, in response to a city of Samaria refusing Him entrance and His disciples request for His permission to call down fire upon them, He said simply, "You do not know what kind of spirit you are of; for the Son of Man did not come to destroy men's lives, but to save them." (Luke 9:55-56)
Finally, we must consider the Muhammad's greatest contribution to Islam, the Koran. Muhammad's claim of being a prophet rises and falls upon our estimation of the Koran and whether or not we believe it to be the word of God or merely the words and imaginations of Muhammad. In judging the Koran, we first must judge it based on what it has to say about itself. The Koran claims to be the continuation of the revelations given in the Law and the Gospel. It claims to both conform and confirm what was written before. This gives us a simple test as to whether or not the Koran was divinely inspired of or mere human origin. Any deviation or contradiction of the Law or Gospel is enough to condemn the Koran as a mere human production, as not being the very word of God, and as proving that Muhammad was not the prophet as he claimed to be. In judging the Koran, we have looked at the historical accounts recorded in the Koran and the various doctrines it teaches. In almost every case where the Koran recounts a historical event that is also recorded in the Jewish scriptures, the Koran gets it wrong! Similarly, there are many doctrinal teachings that differ and contradict the teachings of Moses, Jesus, and His apostles. Clearly the Koran fails at its own claims to be consistent and conformant to the ancient Jewish and Christian writings. Clearly, based on this evidence alone, we can conclude that the Koran is not the word of God and Muhammad was not the prophet of God he claimed to be.
This is my final conclusion of the evidence provided against the claims of Muhammad and the Koran. I hope you have enjoyed this series and have learned something that will help you better understand the world we live in, the Muslim religion, and the Muslim people themselves. I would very much enjoy hearing your thoughts and comments on this matter as well. Feel free to comment here, like my Facebook page and comment there, or e-mail me directly.