Hello comingjoy,
The truth of the matter is that the Lord doesn't give proof so we can believe; He gives faith! Even if people see miracles happen right in front of their eyes, it will not make them believe, if they are not of God. People are always trying to prove or disprove the Word but even if there is an abundance of proof to say that the Bible is true, people will simply not believe, if they did not come from God. The Children of Israel saw all the plagues in Egypt, miracles in the wilderness, were led by a pillar of fire and a pillar of cloud, yet Jesus said they are everyone dead. Why? Because they disbelieved God through His vindicated prophet, Moses! Amazing but true!
The Bible may have been written by many people but they were all inspired of God. Indeed, the Bible states clearly that all scripture is insprired of God. It is God Himself speaking through these men through the words of the Bible. The Bible also said ye are written epistles. So when your friend sees you, he is seeing the Bible, in a sense.
Having said this, the Lord can use anything to bring someone to him. I trust the Lord will turn his heart to Him.
Trust this is helpful.