Thanksgiving is a combination of being grateful for all of the good that we have in our lives, and having an appreciation for where it all came from.
"Everything good comes from God and God is the source of all good things.
He makes it to rain upon the just and the unjust alike and bestows His mercy on both the wicked and righteous, of His loving kindness there is no limit.
We are made righteous by His mercy and justified by His acts of kindness; all of the good that we may have was bestowed upon us by Him.
Therefore we cannot take credit for any good thing that exists in our lives because all of the good that is in us was bestowed to us by Him.
Seeing that both the righteous and unrighteous have good things bestowed to them by God; what then makes a righteous man righteous?
A righteous man then is only an unrighteous man who acknowledges God and gives thanks for the good things God has given him."