The Bible is not subtle in its calls for thanksgiving. Repeatedly, urgently, and throughout its many books the reader is urged to “give thanks to the Lord, for He is good,” and “in all things give thanks.” In both Old and New Testaments, both Gospels and Epistles, we are urged to consider our blessings, and the character of the One from whom they flow, and to offer praise and thanks in response.
Centuries later, Martin Luther described gratitude as “the basic Christian attitude” and the Puritan theologian Jonathan Edwards asserted that a spirit of thankfulness to God was an indicator of one's spiritual state.
Why, one might wonder, is thankfulness so important?
The act of thanksgiving requires both memory and humility -- both reflection on the causes and sources of gratitude, and the recognition of the blessing as a grace, rather than an entitlement. As such, a spirit of thanksgiving is incompatible with pride and distracted self-absorption, two of the greatest threats to spiritual life. It is virtually impossible to be thankful when one is distracted or indignant; thankfulness requires a laying aside of slights and irritations to focus on one's unearned blessings and their source…
(From “Thinking About Thanksgiving,” a 2013 column by Cherie Harder, President of Trinity Forum.)