The purpose of ‘Birkas Hamozon’ is to draw down blessing into the one who is Bentching’s portion of this world. This is because even the Mitzvos become enclothed within material objects such as woollen Tzitzis and leather and parchment for Tefilin.
So, most certainly one of the objectives of ‘Birkas Hamozon’ over physical food items is to draw down blessing into physical objects such as ‘land’ and ‘food’.
We are able to achieve and fulfil the purpose of creation by thanking Hashem and spiritually uplifting the physical world with our Birkas Hamozon on physical food and the physical land. This also brings about additional abundance and additional blessings from Hashem for our physical wellbeing into the actual Gashmius.
This is also why we conclude each of the first three blessings in the ‘Birkas Hamozon’ with a Boruch. This is because the conclusion is like a seal that it should not be interfered with by an outsider. Because since the ‘Hamshocha’ through ‘Birkas Hamozon’ is drawn right down below as mentioned, there needs to be extra care that it should not be interfered with by an outsider. It is explained in Chassidus that the reason why blessings end with a “Boruch” is analogous to when one writes a letter, he seals it to ensure no outsider will read the letter upon its journey to the receiver of the letter. So too is it with our blessings - we want that they should have an effect, but we are also weary that Hashem’s sustenance to us shouldn’t fall into the wrong places, namely, the “Sitra Achra” {literally ‘the other side’ referring to evil forces}. The reason why this seal is so vital in regard to Birchas Hamozon is because on the more supernal spiritual levels the Sitra Achra has no access and therefore there is no chance that it can nurture from holiness.
