The two basic points are 1) every religion has a valid political dimension 2) every religion has suffered from being harnessed to political interests which have no basis in religion.
Buddhism has a valid political dimension. The Buddha gives clear advice to rulers in the Kutadanta and Cakkavatti-Sihanada Suttas. Islam and Judaism have more obvious political dimensions because both Mohammed and Moses were law-givers. The Qur’an and Torah both provide the bases for legal systems to govern polities of various shapes and sizes.
The Qur’an and the Torah both combine the eternal and the temporal, and this reveals the nature of politics. God is eternal and Truth is eternal, but the actual, temporal conditions in which man finds himself are far from God. Man must find a way back to God so, through the prophets, God reveals His spiritual truths and His laws for good-living.
Politics is an aspect of humanity’s collective striving for good. In our political activity we should be guided by the religious truths to which we are the heirs, but we must not make the mistakes of over-literalism, dogmatism, sectarianism, etc. which have so bedevilled our civilisation.
Within the Islamic world the Islamist tendency over-emphasises the political dimension of Islam at the expense of the spiritual. Because it is has lost connection with the loving aspect of God it is prepared to contemplate or perform violence and terrorism to accomplish its sectarian goals. Islamism has more in common with Trotskyism than it does with Islam.
Although Islamism is a corruption of Islam, this does not mean that Muslims should withdraw entirely from the political sphere. On the contrary, it is important that Muslims who are in touch with the spiritual heart of their religion should be socially and politically engaged, in order to reduce the space available to Islamists. Muslims have an important role to play combating the ever-strengthening tide of greed, materialism, addiction, violence and environmental destruction. Organisations like Christian Aid provide an example of how religious people can make vital contributions if they engage with the key political issues of our time.