"If there appears among you a prophet or a dream-diviner and he gives you a sign or a portent, saying, ‘Let us follow and worship another god', whom you have not experienced - even if the sign or the portent that he named comes true, do not heed the words of that prophet or dream-diviner. For the Lord, your God is testing you to see whether you love the Lord, your God with all your heart and soul" Deuteronomy 13:2-4

These verses have been taken to address the question of whether God might ever have intended Israel to worship other beings, say the sun and the moon (No!). They can also be applied to a more pressing (for us) question - can we know the word of God?

Like Rabbi Joshua in the well-known talmudic story of Rabbi Eliezer and the Carob tree, Moses discounts the endorsement of miracles. Impressive as a walking tree might be, it cannot validate the word of God, even if God Himself enables the tree to walk (as must be the case).

More significant are our own powers of reason. If the commandment in question flies in the face of everything we know about God, then we should probably be sceptical. Yet even this is problematic. God does sometimes make counter-intuitive demands, such as telling Abraham to sacrifice his son.

Perhaps then, we should follow not the spoken word, such as voices of prophets or dream-diviners, but only what is written in a legitimate source, such as Deuteronomy itself? Yet this too is problematic.

In the verses immediately preceding ours, God condemns child sacrifice. Had Abraham read Deuteronomy 12:31, would he not have reasoned that the command to sacrifice Isaac must be "false"? We could continue, but the point is clear.

On this reading, at least, our parashah cautions against that most dangerous of all inclinations - the desire for absolute certainty about what God "wants" and the "true" interpretation of his written word.