If I were to speak your kind of language, I would say that man's only moral commandment is: Thou shalt think.
But a 'moral commandment' is a contradiction in terms. The moral is the chosen, not the forced; the understood, not the obeyed.
The moral is the rational, and reason accepts no commandments.

For the New Intellectual: The Philosophy of Ayn Rand (50th Anniversary Edition) (ed. Penguin, 1963) - ISBN: 9781101137680