Mesiras Nefesh, as well as showing our gratitude, gives Hashem great pleasure.
One who offers a Korban for Thanksgiving. The Torah is teaching the laws of the Korban Todah, giving a thank you to Hashem for something He has done good for the person. The Gemara Berachos 54b says.
Four must offer thanks to God with a thanks-offering and a special blessing. They are: seafarers, those who walk in the desert, one who was ill and recovered, and one who was incarcerated in prison and went out. All of these appear in the verses of a psalm (Tehilim 107): Give thanks to the Lord because He is good, for His kindness is eternal. Then it says: They shall give thanks to the Lord for His kindness and for His wonders to the children of men. This Posuk is repeated four times. Today, since we don’t have a Beis Hamikdash, we show our thanks with the blessing of Hagomel.
The Midrash Vayikra Rabbah 9:7 says: In the future, when Moshiach comes, all the offerings will be abolished, but the thanks offering will not be abolished. All the prayers will be abolished, but the Thanksgiving prayer will not be abolished. That is what is written: “The sound of gladness and the sound of joy, the sound of a groom and the sound of a bride, the sound of those who say: Give thanks to the Lord of hosts... which this is the thanksgiving prayer; 'bringing thanks offerings to the House of the Lord' (Yermiah 33:11), this is the thanks offering. Likewise, David Hamelech says: 'I will fulfill the vows I made to You; I will pay thanks to You' (Tehilim 56:13). Todos is written here: Thanksgiving and a thanksgiving offering.
We find in the Megillah: Chazal in Yerushalmy and in Midrash state that all Yomim Tovim will be abolished when Moshiach comes, except Purim, which will still be celebrated. The Rambam Hilchos Megillah says that when Moshiach comes, all the writings of the prophets will be abolished; however, Megilas Esther will still be read as the five books of the Torah. The Rambam continues even though it says that all our agonies of the exile would be forgotten; we would still remember Purim. To understand why Purim is so significant, we must look at what happened when Mordechai asked Esther to go to Achasveirosh to plead for the Jews. She answered that if she went without being invited, she would be put to death. Mordechai answered her: The only way Hashem would save the Jews is with Mesiras Nefesh; go sacrifice your life. Esther followed his command. And it came to pass when the king saw Queen Esther standing in the court, that she won favor in his eyes, and the king extended to Esther the golden scepter that was in his hand, and Esther approached and touched the end of the scepter. And the king said to her, "What concerns you, Queen Esther, and what is your petition? Even to half the kingdom, it will be given to you." The Mesiras Nefesh of Esther was the salvation of the Jews.
We also have the Sages in Berachos 12b, who are of the opinion that we will recite the miracle of leaving Egypt when Moshiach comes. Here too was Mesiras Nefesh, as the Posuk says (Shemos 14:15), when the Yidden were at the Red Sea. “Hashem said to Moshe, Why do you cry out to Me? Speak to the children of Israel, and let them travel. In the explanation in the Chassidishe Seforimis, Hashem told Moshe now was the time to go into the sea with Mesiras Nefesh, and the Yidden crossed the sea and were out of Egypt. There, salvation was through Mesiras Nefesh. This is where Mordechai took his advice from Esther. We know that the highest level of serving Hashem is through Mesiras Nefesh, which gives Hashem great pleasure as well as showing our gratitude. Therefore, the Hagadah and Megilas Esther will be eternal even when Mashiach comes. There is another great act in which Hashem has great satisfaction, and that is by thanking Hashem for what he has done to us. Hence, we will leave our exile and begin to see the great miracle that Hashem did by splitting the sea and the miracle of Purim, as well as the thousands of other decrees that were nullified that only Hashem knows. We recite in the Haggadah: "For not only one arose and tried to destroy us, but rather in every generation they try to destroy us, and Hashem saves us from their hands." Therefore, we would then thank Hashem for all the miracles, and as we would realize more and more the scope of salvation, we would continue to thank Hashem. That is why the Korban Toda and the prayer of thanks will continue after the coming of Moshiach.
Hakaras Hatov showing gratitude is a Midah from Yidden, which is great satisfaction to Hashem. David Hamelech Chapter 100 wrote the Mizmor Lesoda to give thanks to Hashem. The Rabbeinu Bachya in Beshalach says that if a person doesn’t show Hakaras Hatov to another person, he doesn’t have the credentials of a Jew! (Yehuda Z. Klitnick)
