Jesus healed ten lepers and only one came back to give thanks: He said, "Where are the nine?" Romans 1:21 talks about people knowing God (though not in a saving way, of course) and neither being thankful nor giving Him the glory--"so their foolish hearts were darkened" and consequently "God gave them up." Truly sober words and a word to the wise is sufficient. About giving thanks, what if you have a meal for a guest and he was to say afterward, "How much do I owe you?" Wouldn't you be insulted? We can't pay God back even for all eternity to do it. The psalmist says in Ps. 116:12, "What shall I render to the Lord for all His goodness to me?"
Lincoln said the greatest gift God has given a man is the Bible and he said it was the greatest cure for depression. The Great Hallel (Ps. 136) exhorts us to give thanks unto the Lord several times as does Ps. 107 ("Give thanks unto the Lord, for He is good, His mercy endures forever"). Whey gives thank you might venture to ask. Just as there are benefits to being a veteran like health care and the G.I. Bill and there are fringe benefits to a job, there are benefits to being joint-heirs with Christ and heirs of God. "And do not forget all His benefits," says Ps. 103:2. We thank God for who He is and for what He has done (as recounted the history of Israel in Psalms 78 and 105, and the praises of the Great Hallel. "The Lord has done great things for us; whereof we are glad" (Ps. 126:3). Most importantly, we thank God to gain entrée into His presence per Ps.100:4, which says, "Enter His gates with thanksgiving, enter His courts with praise."
I cannot help but be reminded of the following hymn: "Count your blessings, name them one by one, and you will see what the Lord has done." We are to thank God in all things (1 Thess. 5:18), for all things (Eph. 5:20), and with thanksgiving let our requests be made known unto God (Phil. 4:6). A friend of mine has a daughter that complained about the pain in her foot and he told her to thank God for blessing her foot! What faith! God turns curses into blessings and makes the wrath of God to praise Him (Ps. 76:10). The key to a Spirit-filled walk is to be "abounding in thanksgiving" (Col. 2:7). Finally, the offering of sacrifice makes us acceptable to God (Lev. 22:29), and is considered a thank-offering or a sacrifice of thanksgiving. Jonah offered sacrifice with a "voice of thanksgiving." "The one who offers thanksgiving as his sacrifice glorifies Me," says Ps. 50:23. In heaven, the elders and angels will offer thanksgiving to God: "Amen! Blessing and glory and wisdom and thanksgiving and honor and power and might be to our God forever and ever! Amen" (Rev. 7:12).
The best biblical example of contentment and thankfulness for God's provision despite matters is in Habakkuk 3:17-18: "Though the fig tree, not blossom...yet I will rejoice in the Lord, I will joy in the God of my salvation." We must learn to be content in all circumstances just like Paul in Philippians 4:13. Ever hear of the man without shoes that became thankful when he saw a man without feet? How about the father who took his son to a third world country to show them how they live to teach him gratitude, and the son was impressed that they didn't have fences! I'm sure you can think of examples galore for this blessed day. Soli Deo Gloria!