The Mark of the Beast in Ezekiel 9

The vision draws extensively from the Old Testament and you really need to know your Old Testament prophecy to figure out revelation. In Ezekiel 9, we see God putting a mark on the righteous people of Jerusalem to protect them from the coming devastation that is carried out by angels. The protecting angel is putting a pair of crossed lines on the forehead of all the righteous men. He's putting a cross on their foreheads. And this was noticed by the early church fathers that the people in Ezekiel, the righteous ones are being marked with the sign of the cross. It's echoed in Revelation. When you start reading chapter 14, John says, then I saw another angel ascending from the rising sun with the seal