Another thing, why does it say, "for His mercy endures forever"? The Lord does not show mercy to Israel for a year or two, but forever. And similarly, you can see that Moses gave them the Torah, which is called mercy, as it says (Proverbs 31:26), "She opens her mouth with wisdom, and on her tongue is the law of kindness." And it was not taken away from them forever, but given to them as an inheritance, as it says (Deuteronomy 33:4), "Moses commanded us a law, as an inheritance of the congregation of Jacob."
And similarly, all the mercies that He did with them are forever, as it says (Lamentations 3:22), "Through the Lord's mercies we are not consumed, because His compassions fail not." "Oh, give thanks to the Lord, for His mercy endures forever." Another thing, "for He is good." [An analogy:] It is like a homeowner who used to lend to all the people of his city, and the people of his city would say, "Remember that homeowner for good, for he gives us all our needs during the rainy season."
However, during the hot season, he would take three rocks from them. One person came and said, "I will give you everything in one rock." They left the first one and thanked the second one. Then one person came and said, "I will give it to you for free."
Therefore, it is appropriate to give thanks to one who gives for free. Thus, the Lord sustains His creatures for free, and it is appropriate to give thanks to Him. Therefore, give thanks to the Lord, for He is good