To understand the forty and two months that the beast will reign, we must first find the method of time the Bible declares for prophecy. God says in Ezekiel 4:6 "I have appointed thee each day for a year" And we also find the Bible acknowledges a month to be 30 days long. Because in, Genesis 7:11 we see the rain started on the 17 day of the 2nd month and in Genesis 8:3,4 we find the water receded at the end of 150 days, then it says the ark rested on the 17th day of the 7th month. That's exactly 5 months. If we divide the 150 days by the 5 months you get 30 days per month. So 42 months multiplied by 30 equals 1260. According to Ezekiel 4:6, that's 1260 years that Papal Rome would reign.