A true religion would possess holy books or teachings which apply to modern situations. While many Christians, for example, are strongly pro-life, their position finds no explicit support in scripture: although it goes into great detail about other sex-related sins, the Bible never even mentions abortion. Likewise, the churches that oppose cloning and genetic engineering cannot find scriptural support for their beliefs except by taking a few vague verses and pulling them out of context, or by making general arguments about what man was and was not supposedly meant to do. On the other side of the coin, the Bible and other holy books contain very detailed rules about issues that are no longer relevant today. The Old Testament contains specific instructions on how to buy and sell slaves, how we should slaughter animals and burn their carcasses in a way that is pleasing to God, and why empires that ceased to exist millennia ago are evil and should be overthrown. What religions' holy books discuss problems of the modern world like international terrorism, global warming or ecological destruction, much less warn us about problems we have yet to face? A religion authored by an omniscient God would never stop giving useful advice and applicable rules of morality; a religion authored by primitive, pre-scientific peoples would contain much discussion of the problems they faced and little or nothing of the problems to come, which they could not possibly have foreseen.

Taken from "One True Religion"