The Covenanters' Grace

Long before it was popularized as "The Selkirk Grace" by Robert Burns, this saying was often recited "in the south-western province of Scotland before the days of Burns. [It was] always called the Covenanter's Grace" (Robert Chambers, Select Writings of Robert Chambers, Vol. 7, p. 317):

Some hae meat that canna eat,
And some wad eat that want it;
But we hae meat, and we can eat,
For which the Lord be thankit!