Sin means to deviate from that which we are devoted to.
This can have completely metaphysical and divine connotations or completely secular and material ones, it makes no difference in its relevance.
When you truly devote yourself to something you must consider every moment and action that doesn’t coincide with your own mastery or understanding of that something as a sin.
Not always against a God, but against yourself, your Highest self.
The God within you; the God you’re becoming.