One thread of thanksgiving we find throughout scripture is how God reminds us to be thankful even in the darkest of days. A prime example is Jeremiah, who not only gave prophesy after prophesy of judgment against Israel; he had to watch it happen. But God reminded him that is not the end of the story. Jeremiah30:

18 “Thus says the Lord:
Behold, I will restore the fortunes of the tents of Jacob
    and have compassion on his dwellings;
the city shall be rebuilt on its mound,
    and the palace shall stand where it used to be.
19 Out of them shall come songs of thanksgiving,
    and the voices of those who celebrate.
I will multiply them, and they shall not be few;
    I will make them honored, and they shall not be small.
20 Their children shall be as they were of old,
    and their congregation shall be established before me,
    and I will punish all who oppress them.
21 Their prince shall be one of themselves;
    their ruler shall come out from their midst;
I will make him draw near, and he shall approach me,
    for who would dare of himself to approach me?
declares the Lord.
22 And you shall be my people,
    and I will be your God.”

As we look at this promise, God refers to the Prince, this ruler who would come out from them. Notice what He says: "I will make Him draw near, and he shall approach me, for who would dare of himself to approach me?" Who, on their own, is good enough to approach God? No one, except a person of the Godhead. He is talking about Christ, our great High Priest, coming before Him on our behalf. That is what makes us able to be His people, who have a personal relationship with God. And, as we have seen, and will see more of in our call to thanksgiving, that is the reason to let the thanks come out: Who God is, what He has done, and that He has called us to be His.