Your co-workers are making a claim which is hard to support of disprove because it is completely a matter of opinion. Basically they are saying that Islam is better than Christianity and that it will eventually replace Christianity. Muslims believe that Muhammad is the final and greatest prophet. They say that Jesus is a prophet as well, but that Mohammed is an even greater prophet. Of course that is their opinion, but obviously you do not accept this opinion.
Let me tell you a few reasons I believe this is not a valid claim. First of all, let me compare a few facts about Jesus and Mohammed. Jesus was born of a virgin. Jesus never sinned. Jesus raised Lazarus and several others from the dead. Jesus healed the blind and the deaf. Jesus fulfilled dozens of amazingly specific prophecies which were made about the Messiah hundreds of years before he lived (for example Psalms 22:16-18, Micah 5:2, Isaiah 53:1-12, Zechariah 9:9, Zechariah 12:7-12 and many others. For more examples see my book From Shadow to Reality www.ipibooks.com), Jesus was a man of peace and love. Even those who are not Christians know that Jesus love, his character and his example is beyond comparison. To top all this off, Jesus was raised from the dead.
Let us compare this to Mohammed. Mohammed worked no miracles. He did not heal the sick or raise the dead. Mohammed did not fulfill any cclear prophecies. Mohammed was a rather blatant sinner. He married more than a dozen women. He took a nine year old little girl as a wife. He forced his relative to divorce a woman so that he could marry her. He had hundreds of Jews massacred in Medina. He was a pillager and robbed many caravans. His bad temper was legendary. Even Islamic scholars admit that Mohammed had a temper. Mohammed was not a teacher of love and peace, but instead preached war and violence in his name.
So, some Muslims may believe that Mohammed is better than Jesus, but I definitely do not agree. Jesus had a superior message and a superior life. Then there is the comparison between the Bible and the Quran. I have read both. The Quran has many obvious historical errors and blatant contradictions with the Hebrew scripture, as well as rather obvious scientific errors (see the power point on Islam at my web site for a few examples). It is really rather boring and hard to follow. It is not proved by any fulfilled prophecies. It is confusing because sometimes it says Jews and Christians are good, while other times it says that Jews and Christians should be killed. It says that Jesus is a prophet, yet does not agree with what he taught. It advises husbands to beat their wives if they are not obedient. It contains dozens of commands to make war and kill enemies. The Bible has so many proofs of inspiration, including fulfilled prophecies, accurate history, scientific proof. You can find examples of all of this by looking around at my web site or by getting a copy of my book Reasons for Belief (www.ipibooks.com)
One more thing. This is a comparison of the view of God in the Quran and the Bible. In the Quran, God is distant from mankind. In Islam, we must approach God based on our own good deeds. There is no grace. There is no sacrifice for sins. In Christianity God is a loving Father who reaches out to us. In Islam we reach out for God. In Christianity God reaches out to us. God offers us forgiveness for sins through coming to earth as his Son to die and bring forgiveness. There is no assurance of salvation in Islam, but only the hope that maybe one can go to heaven. Christianity is a religion of love and of compassion. Islam is a religion of obedience, but not one of love.
Your Muslim friends can claim that Islam will replace Jesus. I sure hope they are wrong, because Christianity is a vastly superior religion. Not only that, but Christianity is true. It is not a false man-made religion as proved by the obvious inspiration of the Bible. Christianity is validated by Jesus when he was raised from the dead. Bottom line, the Quran is not truth. You should not be intimidated by your friends. They are wrong. They are just expressing their opinion, with no evidence to support it.
I could say a lot more, but hopefully this gives you a little to go on.
John Oakes, PhD