Personally - many Christians describe a personal love of Israel, which often develops when they travel to the land.For millions of Christians, the Bible has come alive on visits to Israel, which they describe as the "trip of a lifetime." It is only natural that they would return home as supporters of Israel.
Practically - there are many reasons to support Israel, as it is making the world a better place. Israeli technologies in science, medicine, high-tech, agriculture, and science are changing lives all over the world. Anyone who uses a cell phone or visits a hospital is a direct beneficiary of Israeli innovation.
Morally - once Christians learn of the very sad history of Jewish-Christian relations and the centuries of Christian anti-Semitism they are often sorrowed and seek to establish a new relationship with the Jewish people. Working together in support of Israel is one way for Jews and Christians to work together in mutual respect.
Politically - many Christians feel that it is important to support the only democracy in the Middle East - a country that shares our values and believes in freedom of speech, freedom of worship, and human rights. As a wave of revolution and instability sweeps across the Middle East, Israel is an island of stability - and the only country where a Christian minority is thriving.
Theologically - Bible-believing Christians may also support Israel because of their reading of the scriptures. God has brought the Jewish people back to their homeland in fulfillment of His promises. Christians want to bless them and help them. They interpret God's promise to bless those who bless His people as an invitation to bless and support that which He is doing.
Learn more:
Why We Support Israel by Susan Michael, ICEJ, 2000
The Israel Test by Rev. Malcolm Hedding, February 2012
Christian Zionism - The Real Story, Friends of Israel Editorial, May/June 2012
My Heroes Have Always Been Hebrews by Joe Carter, First Things, February 2011
HHCC-CJCUC Statement on Christian-Jewish Relations
Why I Stand With Israel by William J. Bennett, Empower America, May 2002