From his book God in Search of Man:
Man had to be expelled from the Garden of Eden; he had to witness the murder of half of the human species by Cain out of envy; experience the catastrophe of the Flood; the confusion of the languages; slavery in Egypt and the wonder of the Exodus, to be ready to accept the law.
It may make me sound Neanderthal to some, but I have to admit that before reading those lines (quite recently) I’d never thought about it that way; i.e. that the law was given at Sinai because at that time and in that place were a people who were actually uniquely ready to accept it, because of their experience and circumstance (even if, through human frailty, they were also not unprepared to stray from it). By the same token, Heschel is highlighting the notion that previous to this there was not a people ready to accept the law.
Even those who don’t necessarily read the earliest chapters of Genesis (the Garden of Eden, Cain and Abel, Noah) as literal history should be able to appreciate the import of this idea. Among the many things humans wonder when we contemplate God is why He acts on His particular schedule—it being one which can appear so arbitrary to us. Why has revelation unfolded as it has over the past three thousand years or so? Why not before? Or why not later? So the startling thing in Heschel’s construction for me is the simplicity of this answer: Because God acts when the time is right. The time is always right for God, I suppose, because God transcends time, but His revelations come when the time is right for humans, who live instead by the signs and seasons He ordained.
It could hardly be argued, for instance, that the time turned out to be wrong at Sinai, to give the law to Moses. It would have been wrong had the Israelites been completely uncomprehending of it, or completely hostile to it, and had left it to blow away in the desert sand. But that’s not what happened, and the law given then has instead resonated through not only Jewish but all of human history.
Well—this is a subject way too big for Yours Truly, but perhaps a musing short enough to keep it within respectable bounds.