Religion is not theism.

Theism is belief in a deity. There is theism without religion, and there is religion without theism.

Religion is a set of laws.

From the Latin religae, 'to bind'. Many dialects have the self-same word for 'law' and 'religion', e.g. the Arabic din.

Your religion is a set of laws you bind yourself to.

Moral codes, holy books or reasoned out principles? Adopt some law or deduce your own. You be you, but harm ye none.

Compulsory religion is a set of laws others bind you with.

While separation of Church and State ended threats of physical violence from the Church, the State's law is still compulsory.