[Radek]

I consider it a bug in the game that a ranger cannot join the Temple. He is a native Vine magic caster. The only place where he can train his Vinecraft is the Temple. So why he cannot join? Also, let us note that a ranger is the only class that can join only one guild (the Warrior's Guild).
If you are unpatched then do not hesitate and use the "guild hopping" trick:
1. Let you ranger pretend that he wants to change role to some class that can join the Temple (paladin, warlock, monk). Take the role changing quest.
2. Go to the temple. You can join immediately even if you haven't finished the quest. The fact that you are training for a class that can join suffices. (That's it. It does not work if you are patched.)
3. Let the ranger cancel the training for the new role.
You have a ranger who is a member of the Temple.
If you are patched then the "guild hopping" trick will not work. You cannot join before you become a class which is allowed to join. In this case, you have to plan your role changes. In the case of a ranger, you have to become some class that can join the Temple first and only then become a ranger.