President Lincoln creating the Thanksgiving holiday

The first religious day of thanksgiving at Plymouth may actually have been in 1623—and not in autumn, but in late summer—when the colonists offered up their thanks to God after a six-week drought. Occasional days of thanksgiving were declared throughout the colonial era and into the years of the early republic. But it wasn't until Abraham Lincoln called for late-November Thanksgivings in 1863 and 1864—and used explicitly religious language to do so—that the day became an annual, permanent fixture.

The first observance of the national holiday came one week after the dedication of the Soldiers National Cemetery at Gettysburg. The language of the proclamation by President Lincoln is beautiful and marked by a rare felicity of expression:  (excerpts)

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 cannot fail to penetrate and soften the heart which is habitually insensible to the everwatchful 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. [...]

It has seemed to me fit and proper that they should be solemnly, reverently, and gratefully acknowledged as with one heart and one voice by the whole American people. I do, therefore, invite my fellow-citizens in every part of the United States, and also those who are at sea and those who are sojourning in foreign lands, to set apart and observe the last Thursday of November next as a day of thanksgiving and praise to our beneficent Father who dwelleth in the heavens. And I recommend to them that, while offering up the ascriptions justly due to him for such singular deliverances and blessings, they do also, with humble penitence for our national perverseness and disobedience, commend to his tender care all those who have become widows, orphans, mourners, or sufferers in the lamentable civil strife in which we are unavoidably engaged, and fervently implore the interposition of the almighty hand to heal the wounds of the nation, and to restore it, as soon as may be consistent with the Divine purposes, to the full enjoyment of peace, harmony, tranquillity, and union.  [...]

PRESIDENT LINCOLN'S THANKSGIVING DAY PROCLAMATION, OCTOBER 3, 1863.