The main problem here, is that I believe that your friend has probably spent very little time in serious thought about this. I think that the simplest, most direct route to really cause someone like this to actually think, is to go to Sinai.
Let’s assume, then, that bible as a whole is really just a large collection of the final product of an evolving mythology. What does your friend think is the best, most rational, and most reasonable way to explain the phenomenon of the Sinai revelation? How did the Hebrew culture write such a lie, and actually get all of its society to not only believe it, but to accept a system of religion based upon it?
To refresh his memory, quote from Deuteronomy chapter 4:
9 Only be careful, and watch yourselves closely so that you do not forget the things your eyes have seen or let them fade from your heart as long as you live. Teach them to your children and to their children after them. 10 ** Remember the day you stood before the LORD your God at Horeb**, when he said to me, “Assemble the people before me to hear my words so that they may learn to revere me as long as they live in the land and may teach them to their children.” 11
You came near and stood at the foot of the mountain while it blazed with fire to the very heavens, with black clouds and deep darkness. 12
Then the LORD spoke to you out of the fire. You **heard **the sound of words but saw no form; there was only a voice. 13 He declared to you his covenant, the Ten Commandments, which he commanded you to follow and then wrote them on two stone tablets.
Amongst other places in the bible, this is the only record we have anywhere in any religion which claims that an entire nation of people literally heard a deity speak. Here, and in other references in Scripture, this descending of God to Sinai is used as evidence to support the acceptance of God’s law.
Continue in the chapter:
32 Ask now about the former days, long before your time, from the day God created human beings on the earth; ask from one end of the heavens to the other. Has anything so great as this ever happened, or has anything like it ever been heard of? 33 Has any other people heard the voice of God
a] speaking out of fire, as you have, and lived? 34 Has any god ever tried to take for himself one nation out of another nation, by testings, by signs and wonders, by war, by a mighty hand and an outstretched arm, or by great and awesome deeds, like all the things the LORD your God did for you in Egypt before your very eyes? 35 You were shown these things so that you might know that the LORD is God; besides him there is no other. 36 From heaven he made you hear his voice to discipline you. On earth he showed you his great fire, and you heard his words from out of the fire. 37 Because he loved your ancestors and chose their descendants after them, he brought you out of Egypt by his Presence and his great strength, 38 to drive out before you nations greater and stronger than you and to bring you into their land to give it to you for your inheritance, as it is today.
Your friends task, then, should be to provide a natural explanation for how this type of claim has been made, and how this lie was started. There’s three main courses he would take, all of which have problems, none of which are natural explanations. (We’ll define “natural” as something which can happen more than one time, something which is repeatable.)
These three courses are:
(i) Present lie; the originators of this lie simply made the claim – you just now saw God! – and the hearers stupidly believed it. They then wrote it down for future generations.
(ii) Past lie; some group of people made the claim that they discovered these writings (even though they had just finished writing them), that these writings had been lost, and the Hebrews simply believed them and the writings.
(iii) Future lie; the people making the claim wrote down things which they told their present generation would one day come to pass, and the generation believed them.
The main problem, is that none of these explanations are natural. You must absolutely assume that such explanations occurred and are valid, despite the fact that they would be an example of the only time in human history where such a thing has happened, and therefore not natural. Since such an explanation is based on a singularity, the chances of them occurring are no greater than the supernatural explanation. If you’d like details on all of this, please contact me.