1. An explanation of Purim can be gleaned from the laws of Purim. As our Sages declared, "Whoever works on Purim will never see a sign of blessing."
2. "God will bless you in all you do." This verse constitutes a divine promise of blessing which will come through our actions. Any place where the rabbis discuss the obligation to have faith/trust in God (bitachon) and the intertwined permission of personal effort /will (hishtadlut) - this verse is cited.
And yet it makes sense, that the permission of personal effort - which is broadly applicable - itself branches out from the principle of personal effort in the service of God. If, for example, the performance and fulfillment of mitzvot did not depend upon the personal effort of a person and their spiritual work - then certainly there would be no room for personal effort in the quest for fulfillment of personal needs.
And behold, truthfully there is one mitzvah among the 613 mitzvot that is unique, insofar as it is explicitly stated in the Torah in a way that emphasizes the relinquishing of personal effort. This mitzvah is that of wiping out the memory of Amalek (mchiyat Amalek). Even though we are actively obligated in the wiping out Amalek, nevertheless the Torah expresses aspects of the mitzvah which denote and express this erasure of personal effort. Notably, in the Torah God explicitly says "I will utterly blot out the memory of Amalek". "I will blot out", as opposed to "you shall blot out."
And as there is one mitzvah in the Torah which is expressed as a manifestation of the relinquishing of personal effort, so too the day in which that mitzvah is celebrated similarly should manifest the relinquishing of personal effort. If on every other day of the year we relate to and invoke the principle of "God will bless you in all you do", then on Purim - a day of the celebrating the erasure of Amalek - we abdicate this principle. That is why we are left with such a significant law concerning Purim: "Whoever works on Purim will never see a sign of blessing."
Then God said to Moses, "...I will utterly blot out the memory of Amalek from under heaven!”
לֹא־יִקְשֶׁ֣ה בְעֵינֶ֗ךָ בְּשַׁלֵּֽחֲךָ֨ אֹת֤וֹ חׇפְשִׁי֙ מֵֽעִמָּ֔ךְ כִּ֗י מִשְׁנֶה֙ שְׂכַ֣ר שָׂכִ֔יר עֲבָֽדְךָ֖ שֵׁ֣שׁ שָׁנִ֑ים וּבֵֽרַכְךָ֙ יְהֹוָ֣ה אֱלֹהֶ֔יךָ בְּכֹ֖ל אֲשֶׁ֥ר תַּעֲשֶֽׂה
When you do set either one free, do not feel aggrieved; for in the six years you have been given double the service of a hired worker. Moreover, your God will bless you in all you do.
Therefore, when your God grants you safety from all your enemies around you, in the land that your God is giving you as a hereditary portion, you shall blot out the memory of Amalek from under heaven. Do not forget!
וּמֻתָּר בַּעֲשִׂיַּת מְלָאכָה, וְאַף עַל פִּי כֵן אֵין רָאוּי לַעֲשׂוֹת בּוֹ מְלָאכָה. אָמְרוּ חֲכָמִים כָּל הָעוֹשֶׂה מְלָאכָה בְּיוֹם פּוּרִים אֵינוֹ רוֹאֶה סִימַן בְּרָכָה לְעוֹלָם.
...It is permitted to work on these days. It is not, however, proper to do so. Our Sages declared, "Whoever works on Purim will never see a sign of blessing."