Bitachon When Benching
It is well known that the first bracha of Bircas Hamazon was instituted by Moshe Rabbeinu. He composed this bracha so that the Yidden should thank Hashem upon receiving the manna in the desert. Even though the bracha was designed for the heavenly bread - lechem min hashamayim - which the Yidden ate while in the desert, we nonetheless continue to make this bracha to this very day after eating.
The question is asked, if the bread we eat today is not from the heaven anymore, rather we work and toil for the sustenance, why then do we say the same after-bracha that was made on the bread from the heavens?
The truth of the matter is that all of our sustenance comes directly from Hashem, not only when it was clear that Hashem was providing for us, but throughout all the generations starting from when the Yidden entered Eretz Yisrael, the success that the Yidden experienced in earning their livelihood was because Hashem was blessing their endeavors.
Although it wasn't in the same form as when the Yidden were in the desert, for then the bread literally came directly from above, it was nonetheless the same source, the difference expressed itself simply in how it arrived i.e. through our work, and in which form we receive our livelihood, certainly not the form of the manna.
This is why we continue to recite the bracha that Yidden recited in the desert on the manna from the heavens, because today as well essentially all of our sustenance is directly from Hashem, just like then. The only difference is that now we have to put in some real effort, but because the effort is put in only due to Hashems command, not because we really feel that it's necessary the effort therefore is clearly secondary.
When we focus on this, and have this kavana - intention- while reciting the first bracha in Bircas Hamazon, this message will certainly be internalized, and it will have an impact on how we view our work to earn a livelihood.
This will result in our always being relaxed, with Menuchas hanefesh, because it is clear that Hashem is our main source of parnoso, and His track record shows that He will come through.