Here are a few quotes of our Founders and President Lincoln proclaiming Thanksgiving Celebrations to our Creator and Almighty God. There is no hint whatsoever that there was any "Separation" between Church and State that was promoted or intended by our Government before the past 70-80 years.
These Patriots founded our Christian Nation with the help of our Creator who they continually praised and sought for guidance, protection and blessings.
These qoutes are taken from David Barton's "Celebrating Thanksgiving in America"
"Whereas it is the duty of all nations to acknowledge the providence of Almighty God, to obey His will, to be grateful for His benefits, and humbly to implore His protection and favor. . . . Now, therefore, I do recommend and assign Thursday, the 26th day of November  . . . that we may all unite to render unto Him our sincere and humble thanks for His kind care and protection." George Washington
"[Congress] recommended [a day of] . . . thanksgiving and praise [so] that . . . the good people may express the grateful feelings of their hearts and . . . join . . . their humble and earnest supplication that it may please God, through the merits of Jesus Christ, mercifully to forgive [our sins] and . . . [to] enlarge [His] kingdom which consisteth in righteousness, peace and joy in the Holy Ghost. 24 Continental Congress, 1777 – written by SIGNERS OF THE DECLARATION SAMUEL ADAMS AND RICHARD HENRY LEE"
"[I] appoint . . . a day of public Thanksgiving to Almighty God . . . to [ask] Him that He would . . . pour out His Holy Spirit on all ministers of the Gospel; that He would . . . spread the light of Christian knowledge through the remotest corners of the earth; . . . and that He would establish these United States upon the basis of religion and virtue." GOVERNOR THOMAS JEFFERSON, 1779
"[I] appoint . . . a day of public thanksgiving and praise . . . to render to God the tribute of praise for His unmerited goodness towards us . . . [by giving to] us . . . the Holy Scriptures which are able to enlighten and make us wise to eternal salvation. And [to] present our supplications...that He would forgive our manifold sins and . . . cause the benign religion of our Lord and Savior Jesus Christ to be known, understood, and practiced among all the inhabitants of the earth." GOVERNOR JOHN HANCOCK, 1790
"The year that is drawing toward its close has been filled with the blessings of fruitful fields and healthful skies. To these bounties, which are so constantly enjoyed that we are prone to forget the Source from which they come, others have been added which are of so extraordinary a nature that they can not fail to penetrate and soften even the heart which is habitually insensible to the ever-watchful providence of Almighty God. . . . No human counsel hath devised nor hath any mortal hand worked out these great things. They are the gracious gifts of the Most High God, Who, while dealing with us in anger for our sins, hath nevertheless remembered mercy." Abraham Lincoln 1863