Thanksgiving, a purely secular holiday, is a time when we pause to reflect on all the things we are thankful for. This is impossible without acknowledging something or Someone other than ourselves for the things we appreciate in life. Being thankful is realizing a debt we owe, an act of humility. Humility is impossible without God.
In the Holy Sacrifice of the Mass, after the reading of the Sacred Scriptures, we reply "Deo Gratias-Thanks Be to God" Thanks Be to Him Who humbled Himself out of love for His creatures to become one of these very same creatures! For just this act alone, we could never Thank Him enough, but He still wanted to prove to us the depth of His love by Redeeming us with His own Precious Blood. And still He wasn't finished. In order to be completely and utterly united with us, He gave His very own Flesh to be our Food, so that we could be intimately united with Him everyday if we so wished: Eucharist, which means "Thanksgiving". Every time we receive Our Lord in Holy Communion we should be making a profound act of Thanksgiving.
"Thank You O Lord, for these Thy gifts, which we are about to receive from Thy bounty" ~Traditional Prayer before Meals