"B-reishis" = the world was created for the sake of reishis, the "reishis pri ha'adamah," the first fruits of bikurim which the farmer brings to the Mikdash, as described in the opening to our parsha.
I don't mean to minimize the importance of bikurim, but let's be real -- if you asked 100 people to pick one mitzvah for which the world was created, most would answer things like learning Torah, saying shema, emunah. Not bikurim. What do Chazal see as so crucial in the mitzvah if bikurim?
When the farmer brings bikurim to the Mikdash in essence what he is saying is, "It's not me." He may have plowed the field, he may have planted the seeds, he may have weeded, watered, tended the crops, and finally harvested, but the crops are not the product of his work alone. By bringing bikurim the farmer is saying that it's not "kochi v'otzem yadi," but rather his success comes from Hashem.
"V'lakach ha'kohen ha'teneh mi'yadecha" -- bikurim takes the fruit out of being "mi'yadecha," the work of your hands (alone), and acknowledges that it is a gift from Hashem.
"Lo achalti b'oni mi'menu" -- R' Shimon Sofer explains that the word "oni" can be interpreted as strength. Ya'akov describes Reuvain as "kochi v'reishis oni," my first strength. Again, the farmer is declaring that the fruit does not come from the strength of his labor, but rather is a gift from G-d.
What Chazal are telling us is that G-d created this thing we call "earth" with laws of nature that serve to obscure his presence and where humans can delude themselves into thinking they are in total control in order so that we might have the opportunity to make the biggest kiddush Hashem possible -- to pierce that veil and declare that Hashem is behind it all. Even if there was no physical world there could be angels who learn Torah, who say shema, who have emunah. You don't need a world for that. All that can take place in Heaven. What you need a world for is so that we can declare, through our bikurim, that G-d is present even where he doesn't seem to be.
The Torah uses the term "higadti" when describing the farmer's speech to the kohen. Normally the term hagadah, as opposed to amirah or dibur, connotes harsh words. The farmer is relating how G-d helped bring us to Eretz Yisrael and his asking for Hashem's bracha -- what's so harsh about what he is saying?
Here we have the kohen, says the Ishbitzer, who lives a holy life, who can cloister himself in the Mikdash, who is involved in Torah (Rambam end of Hil Shemitah) when he is not doing avodah. Along comes a simple farmer with his basket of fruit and barges into that domain of kedusha. You can picture him with his overalls, maybe with the mud from the field still on his workboots, marching up to the kohen and handing over that basket. The farmer then declares to the kohen, "Don't think you have an exclusive on G-d. I may be out on the field working, I may be a simple farmer, but my basket of fruit is as valuable as what you are doing." That's hagadah = kashe k'gidim, harsh words. "Higadti l'Hashem Elokecha..." -- your G-d, reb kohen, is my G-d too. My avodah is at least as valuable as yours. Real holiness is not just when you live a life in the Mikdash, in the beis medrash, the life of the kohen. Real holiness is when you live in the darkness of olam=he'elem, where G-d's presence is hidden, out in the field, out dealing with the struggles of the world, and you come with bikurim and declare that that "real" world is just a fake and what is real is G-d.
Maybe this is what the Midrash Tanchuma means when it teaches that Moshe was troubled as to how we would get by without bikurim when we no longer had a Mikdash. Moshe was not worried about the loss of korbanos or avodah -- holiness. Moshe was worried more about the loss of a place where one could elevate the mundane and make even it holy. That's what bikurim is all about.
Hashem's answer to Moshe was that we will have 3 tefilos a day that will make up for the loss. Tefilah reminds us (especially when you stop right in the middle of a work day for minchah!) that it's not the hard work we do that makes things happen, but it's G-d who is behind it all.