Did Jesus teach separation of church and state? Related: Biblical basis for the separation of church and state


In @Richard's answer on the provided link, he mentioned Mark 12:17 as foundation for Christ teaching separation of church and state.

I was wondering if this is to be taken as doctrine (meaning that the government should always be separated from the Church), or if it should be taken as advice on what to do if government is not united with the Church.

We all know that power corrupts. We've seen it many times in the Old Testament; One particular example of this (off the top of my head) is David, who was a prophet, and a very strong spiritual leader at that.

So, for the actual question:

Are we to understand that Jesus taught separation of Church and state as part of His new Gospel? If not, are we to understand that unification of the Church and the state government is a desirable thing (like in some Islamic states)?

Note:

We have, of course, seen the Catholic Church act as (or have a strong influence on) the government in pre-Protestant times; as we all know, the Catholic Church dealt with a lot of corruption in the leadership, so I don't think this can be taken as evidence of a formal declaration of doctrine.
Richard's answer isn't really teaching for separation of church and state, but rather evidence against fighting it. It shows we are to obey the authorities, but it doesn't say the government cannot be a specific religion. Jesus never taught to keep it separated (that is recorded at least), so it cannot be taken as doctrine. At the same time, he also never preached that the unification is desired.

To have a government that has Christian values would, of course, be desirable (the Bible is considered to be the greatest book of morals ever written by a lot of non-Christians). However, Christianity is about choosing to have a relationship with Jesus. To have a government that forces everyone to be Christian could easily cause a lot of people to conform publicly, but resent Jesus privately. This is why I believe He never tried to make that unification.