Joshua Claybourn has an excellent post on politically active Christians. Nice work! I'm going to expand on it a little bit, reflecting on my past experiences as a member of the Unitarian Universalist Association.
God does not belong to your party: I agree that it is presumptuous to say that God is on our side in a public debate on issues, especially one in a secular context where no one is expected to unconditionally accept Biblical authority. I really respect writers like Robert P. George, who writes in support of traditional values, but without resorting to saying "this is true because the Bible says so". He lays out a good case based on respect for life and reason. Regarding motivation, I think we err if we think that we are doing God a favor by our activism, as if His will would be thwarted if we stopped. No, any political activism we do is for the benefit of our society. God could change our world with a word if He wished. That said, however, I believe we should study and know the will of God, so that we can be sure that we are on His side.
The ends do not justify the means: I remember a couple of years ago, President Clinton and Vice President Gore appeared at a fund-raiser which raised a huge sum of money. While it was a legal fund-raiser, they also took the opportunity to speak out for campaign finance reform (at the fund raiser!). Several donors were said to have questioned the hypocrisy of raising gobs of cash while speaking out against the freedom to do so. Clinton's reply was that it was justified by fighting the Republicans' agenda. He mentioned several Democrat-party objectives: gun control, abortion, his public land grabs. It probably never occurred to him that in a free and democratic republic his political opponents have just as much right to speak out for their views, and raise money for that purpose. If he could have been declared king for life by our Supreme Court, I'm sure he would have been willing to put our Constitution in the shredder to do so.
Faith does not lie in support: To this, I also add that faith does not perform acts of violence, against life or property. People who resort to acts of violence to make a point don't have one.
Generosity does not mean compassion: I could write for hours on this subject, but let me add this one quick point before I have to leave for dinner: Government cannot be compassionate because it has no resources with which to be so. Whatever the government gives to anyone must be taken away from someone else, with some taken away to the bureaucrats who manage our system. Bill Bradley was wrong when he said we needed a more compassionate government; it just isn't so! True compassion is provided by people who give of their own time and money, not those who wish to utilize the services of someone else's wallet.