Why do I need to go to work? If G-d will provide, let me sit at home with my feet up eating chocolate!
The Torah instructs us to live in the sukkah for seven days. Living implies that the sukkah must be a semi-permanent structure. If it is too flimsy, it does not qualify. If it is round it does not qualify. Why not?
The Holy Temple and its structures such as the Altar must be squared at the edges, not rounded. Rabbi Samson Rafael Hirsch explains that things in nature are round. Think about pebbles or tree trunks.
Man can create objects with corners. The fashioning of cornered objects demonstrates our dominion over nature. When we make the Temple items squared, we utilize our unique ability to elevate nature and transform it into spirituality.
When we build our houses, we build them with corners, representing our unique power and dominion over nature. Likewise, when we build our sukkot, they must demonstrate our ability to transform this world. The sukkah demonstrates our trust in the Almighty that He will protect us in the elements. But we must make our effort.
With any blessing that comes from G-d, if we do not do our part to create a receptacle for His blessing, we have no way to receive the blessing. We can pray all day for sustenance, but if we are not prepared to go out and work, we cannot receive Divine assistance.
If we were to simply go out and sleep under the stars, we would lack the receptacle for G-d’s shelter. We need to make our effort by building a sukkah and showing that we are prepared to transform this world and make it a dwelling place for the Holy One blessed be He.
G-d wants to protect us. He wants to bless us. He wants to bestow His bounty upon us. But we must make an effort, an hishtadlus, to create a vessel to receive His blessing. Going out to work, building a semi-permanent structure for the sukkah demonstrates our commitment to transforming nature. When we are committed to transforming nature, G-d is committed to infusing us with the Divine energy to make it happen.