What is the opposite of secular?

The opposite of secular would be religious or spiritual.

Secular means of or relating to the doctrine that rejects religion and religious considerations. Therefore the opposite to this has to be spiritual i.e concerned with sacred matters or religion or the church. The peoples of the world today are basically secular.

The opposite of secular is "theocratic". It means a form of government by God or through a priestly order e.g: France or Pakistan.
Religious.