to the congregations of God

Below are excerpts from some of the relevant articles she wrote relating to Thanksgiving. All emphasis in the quotes are from Sarah Hale.

1837
This may be the first writings Sarah Hale did for the Lady's Book regarding Thanksgiving. She starts her campaign off with God's Holy days.
 

The noble annual feast day of our Thanksgiving resembles, in some respects, the Feast of Pentecost, which was, in fact, the yearly season of Thanksgiving with the Jews. ... induce all the states to join in the commemoration of "In-gathering," which it celebrates. It is a festival which will never become obsolete,
Sarah Hale, Godey's Lady's Book 1837

1857
Sarah quotes scripture that is describing the Feast of Trumpets (though she mistakenly attributes this scripture to Pentecost). Note that her intentions are not simply to express the similarities between God's Holy days and Thanksgiving, but to recreate them in a new “Christian” way. She also clarifies that this is logically necessary because there is no New Testament equivalent for Christians to observe. She even goes so far as to lay aside any fears or concerns for copying these old testaments ideas because they are “approved by God”.

THE NATIONAL THANKSGIVING.

“Then he said unto them, Go your way, eat the fat, and drink the sweet, and send portions unto them for whom nothing is prepared: for this day is holy unto our Lord: neither be ye sorry; for the joy of the Lord is your strength.” - NEHEMIAH viii. 10.

SUCH was the order given to the people of Israel for the celebration of their National and Religious Festival, the “Feast of Weeks.” We learn from this that a day of yearly rejoicing and giving of gifts was not only sanctioned but enjoined, by Divine authority, on God's chosen people. Such yearly festival is not positively enjoined on Christians; but that it is both expedient and beneficial may be safely urged, when we find that the practice was approved by our God and Father in heaven.
...
Our Day of Thanksgiving represents, in many striking coincidences, the Jewish Feast of Weeks; only make our day national, and we should then represent the union of joy that was the grand proof of the Divine blessing.
Sarah Hale, Godey's Lady's Book 1857

1859
Notice the same theme, the connection she's making between God's Holy Days and Thanksgiving.

Dear Lord, our God and Saviour! ... THAT the American People shall have an annual Thanksgiving Festival after the ingathering of their harvests is now a settled matter. Every State and Territory has, in some way, signified its willingness to adopt this venerable custom, which we recognize in the Jewish “Feast of Weeks ,” as appointed by Jehovah for His Chosen People.
Sarah Hale, Godey's Lady's Book 1859

1860
This is the section Sarah highlighted on a page she sent in a letter to President Lincoln. Lincoln later took her advice and declared Thanksgiving a national holiday

Well did that patriot divine, Rev. Charles Wadsworth, exclaim, in his last Thanksgiving sermon- “Thanks be unto God for this American Pentecost! Never were the bonds of our beloved brotherhood so revealed in their strength! Never before did so many sister States keep lovingly together this feast of harvest. It is the gathering of the one great household with offerings of praise to the one common temple- the central Salem of peace- the God of love.”
Sarah Hale, Godey's Lady's Book 1860

1861
This was also sent to President Lincoln, and highlighted. A call is made for a “universal” day for all religions to give thanks to God. Again, a specific declaration that Thanksgiving Day is a “Christian” holiday, and is a copy of the old testament days.

What could do more to arouse and preserve the fraternal feelings which should exist, especially among the nations of Christendom, than the establishment and universal observance of one general Christian Festival of Thanksgiving , on the same day of the year, throughout those nations? All sects and creeds who take the Bible as their rule of faith and morals could unite in such a festival. The Jews, also, who find the direct command for a feast at the ingathering of harvest, would gladly join in this Thanksgiving , ... a universal holiday on the LAST THURSDAY OF NOVEMBER.

The enjoyment of it would be heightened in every land by the knowledge that in all other lands where the Bible was the BOOK of faith, in all places throughout the globe where Christians of any nation or creed could meet together, this happy, hallowed festival was and forever would be kept on the last Thursday of November.

... There is something so cheering and delightful in the idea of a DAY OF UNIVERSAL THANKSGIVING , set apart among all the branches of the Christian family
Sarah Hale, Godey's Lady's Book 1861

1863
She restates her interest in Thanksgiving becoming a mirror image of Pentecost. (Which she is confusing with the Feast of Tabernacles in scripture). She even declares that Thanksgiving is “following the appointment of Jehovah.” It is also important to note that she considers Thanksgiving to be the English “Harvest Festival”, which is also called Harvest Home.

THUS commanded the inspired leader of the Jews, when they kept the “Feast of Weeks;” in a time of national darkness and sore troubles shall we not recognize that the goodness of God never faileth, and that to our Father in heaven we should always bring the Thanksgiving offering at the ingathering of the harvest?
...
Can we not, then, following the appointment of Jehovah in the “Feast of Weeks,” or Harvest Festival, establish our yearly THANKSGIVING as a permanent American National Festival
Sarah Hale, Godey's Lady's Book 1863

1864
Sarah makes it abundantly clear that she believes the last Thursday in November is not a secular national holiday but a religious event. Then she declares that the feasting of Thanksgiving is a copy of the feasting God commanded to us on his Holy Days. Thanksgiving is even described as possibly able to end the civil war and is finally declared to be a “foretaste” of things to come. This is a close description of God's Holy Day plan.

These are sections of a printed article that were highlighted and sent directly to President Lincoln. ( as well as being published in Godey's Lady's Book )

It is the peculiar happiness of Thanksgiving Day that nothing political mingles in its observance. It is in its very nature a religious and domestic holiday.
...
There is one duty connected with the day which on the present occasion should be especially called to mind. In the divine order which was given to the Israelites for the celebration of their great National Festival, the “Feast of Weeks, “they were bidden to “eat the fat, and drink the sweet, and send portions unto them for whom nothing is prepared.” ... Let us each see to it that on this one day there shall be no family or individual, within the compass of our means to help, who shall not have some portion prepared, and some reason to join in the general Thanksgiving.
...
We may even hope that for one day war itself will cease by common consent, as was the custom in the Middle Ages during the solemn church Festival known as the “Truce of God;” and it is not impossible that sentiments may then be awakened which will aid in bringing on that return of true union and peace which is so earnestly desired.
....
Let us all, with devout thankfulness to the beneficent Giver of all good gifts, do our best to make this coming Thanksgiving Day a foretaste of that happy period of “peace on earth and good-will among men,” in which all wrongs and sufferings from evil are to dissolve like shadows before the noonday sun, in the righteousness and goodness which will crown the glorious reign of Christ on earth.
Sarah Hale, Godey's Lady's Book 1864

Mrs. Hale is the single most important individual in the history of Thanksgiving Day. She pushed for and sought after a holiday that was to replicate God's holy days with a new form of worship, a “new testament” version of God's “old testament” holy days. A universal day for all Christians to observe together.

The opportunity is now presented for a cordial and universal enjoyment of this festival in the United States. And when our Christian temples of worship are crowded on Thanksgiving Day, and from every altar goes up the sacrifice of faith and love, prayer and praise, to the only living and true God, will not the nations of the Old World learn and confess that America is a Christian Nation?
Sarah Hale, Godey's Lady's Book