When accounting for income taxes, the differences between financial accounting and taxation accounting creates permanent and temporary differences between the expenses and liabilities reported under each regime. Why do these differences exist? What are the reasons that explain why we have one system of accounting for financial reporting, and a second for taxation? Please give an in-depth explanation for the various reasons for why there are two systems for this, instead of one.

I am looking for a general explanation for why we have the two systems. Basically I want to know why there is a system for accounting finances and for accounting tax, not just the rules but the meaning for the separation.