What was the main functions of the Knights Templar?

The Knights Templar, also known long ago as "The Poor Knights of Christ and the Temple of Solomon," were a quasi-military group formed in the early twelfth century by European Christians early in the Crusades. The Knights took their name from their original headquarters, which was in the Temple Mount, near the site of King Solomon’s Temple.
Their original function was to protect Christian pilgrims on their way to the Holy Land. These pilgrims were being harassed and slaughtered by outlaws on the road. During the Crusades, the Knights' functions expanded. Sometimes they accompanied armies into battle, and they are particularly famous for their role in helping the Kingdom of Jerusalem win the Battle of Montgisard.
But they are perhaps most notably known for establishing a financial system that aided pilgrims on their journey. Pilgrims would deposit money or valuables with the Knights, then receive a document stating that value, which they then could redeem in the Holy Land. This protected their assets from outlaws on the road. This was perhaps an early precursor to a banking system.
Once the Crusades were lost by the Christian side early in the thirteenth century, the Knights diminished in importance. Many of the Knights were eventually arrested, and some executed, as European royalty sought control over them.