The correct answer to this open question is the following.
The phrase from Thanksgiving proclamation that most clearly supports the Christian faith is "And also that we may then unite in most humbly offering our prayers and supplications to the great Lord and Ruler of Nations and beseech him to pardon our national and other transgressions."
It was US President George Washington's idea to name one day in November as the Proclamation day for Thanskgiving. It was decided that on the 26th of November, American people should dedicate that day to pray and give thanks for their lives in the United States. This decision was made on October 3, 1789. Years later, President Abraham Lincoln ratified this important celebration date for Americans, but with a slight change. It was going to be celebrated on the last Thursday of November.