The offender may already have been pronounced guilty by the rulers (see Exodus 18:21-22), and the case was referred to Moses in order that the punishment might be awarded by the divine decree. No law had as yet been enacted against blasphemy except by implication. See Exodus 21:17; Exodus 22:28.

And they put him in ward,.... In some prison, a place known in the camp, as Aben Ezra observes:
that the mind of the Lord might be shewed them; for, though this was a breach of the third command, in which God declares he would not hold such an one guiltless, Exodus 20:7; yet no particular punishment being expressed, it was not a clear case whether the Lord would punish for it himself, by an immediate stroke of his hand, or whether by the civil magistrate; and if by the latter, in what manner; for though it might be concluded, without any hesitation, that he was worthy of death, since cursing father or mother was death, Exodus 21:17; and much more blaspheming God, yet what death to put him to they might be at a loss about; or if that was understood of stoning, they might think this deserved a sorer punishment, and therefore consulted God about it.

That the mind of the Lord might be shewed - For God had only said in general, that he would not hold such guiltless, that is, he would punish them, but had not declared how he would have them punished by men.