There is a dispute as to whether a rabbinic prohibition or mitzvah has the same metaphysical import as a Torah one, or whether it's pragmatic.
Rav Meir Simchah haKohein miDvinsk (Meshekh Chokhmah, Devarim 17:11) holds that Torahitic prohibition describes something that is inherently wrong. The universe is made such that combining meat and milk is a problem (metu’af, meshuqatz). A rabbinic prohibition lacks that reality. Even though the rabbis prohibit the mixture, chicken and milk isn’t inherently damaging. Rather they pragmatically realized that allowing it had led to error through habit or accident. Therefore, one needn’t the same care when dealing with rabbinic extension as when dealing with the damaging or refining thing itself.
Another example is shemittah today, which is rabbinic. Torahitic shemittah comes with a blessing that Hashem will insure sufficient crops in the 6th year for the 6th, 7th (when there is no farming) and 8th years (waiting for the replacement crops to arrive). However, Torahitic yovel and shemittah only apply when most Jews live in Israel, and according to the Tosafists and others, the majority of tribes live on their tribal lands. Meanning that today, and in fact ever since 10 of the tribes were lost in the First Temple period, shemittah is rabbinic. Is there still a berakhah attached?
The Seifer Me’iras Einayim (SM”A, Ch”M 67, #2) someone who keeps rabbinic shemittah today gets no such guarantees. This is in theological agreement with the Meshekh Chokhmah.
The Chazon Ish (Deshevi’is 18, #4), however, writes that the blessing did apply during the 2nd Temple and after its destruction, for the heavenly court fulfills based on what’s decreed down below.
There is a similar statement by Lubavitch's Alter Rebbe. In a rare case of where the Shulchan Arukh haRav discusses the purpose of a law rather than just codifying practice, he discusses the significance of the second day of Yom Tov that is observed by those outside of Israel.
He explains that there is no time in the heavenly realms. The supernal “Pesach” is not associated with any particular time. Hashem made a connection between that Pesach and the 15th of Nissan, giving us a worldly manifestation within time. The SAhR continues that the 16th of Nissan is connected to the very same supernal Pesach. The seder on the 2nd night is a manifestation of the same metaphysical reality. What differs is who draws down the connection, not what it is we are connected to. Notice that the Alter Rebbe, like the Chazon Ish, believes that rabbinic law creates metaphysical realities, and therefore obeying or violating it can improve or damage the performer and the world.
The pragmaticists would therefore make violation of a Torahitic mitzvah a much worse thing hashkafically, whereas according to the Shulchan Arukh haRav, violating the Torahitic day of rest of Pesach or the Rabbinic one do the same metaphysical damage.
A third position is expressed by Rav Elchanan Wasserman (Qunterus Divrei Soferim), who blurs the distinction altogether. He takes it for granted there is \a reality behind rabbinic statements. It is all revealed from the Creator, all the Ratzon Hashem yisbarakh (the Will of the Creator, blessed be He). The difference between a derabbanan and a de’oraisa is the explicitness. In other words, the rabbinic law existed because they detected a pre-existing metaphysical issue, one more minor than the Torah law, but still worth avoiding; or a metaphysical opportunity worth mandating we take advantage of. Therefore rabbinic law is less sacred, and violation involves lesser realities. A difference of quantity, not quality.
So in short:
1- R Meir Simchah haKohein and the Me'iras Einayim saying there is a qualitative difference in which Torahitic law does things to existence, whereas rabbinic laws are "merely" pragmatic advice to maximize meaningful observance of Torah law.
2- R Elchanan Wasserman who says both have metaphysical impact, but there is a real quantitative difference in the size of the impact.
3- The Alter Rebbe and the Chazon Ish say that there is nothing inherently spiritually different to a rabbinic law's fulfillment or violation in comparison to a Torah law.
Related is the question of how doubt is treated. ספק דאוריית להחמיר -- when we have a doubt about whether or not something fits Torah law, we play safe. But ספק דרבנן לקולא -- we are lenient when the doubt is in a rabbinic law.
If rabbinic law is "only" pragmatic, that is unsurprising. There is a limit to how much effort we invest in this secondary layer around the actual spiritual work.
But according to the other opinions?
Perhaps they follow the Ramban, who says that the reason we are stringent in doubts about Torah law is itself a rabbinic law. (The Rambam says something similar to explain ספק ספקא, but this answer is getting long enough.) They did not pass a similar rule about doubts in rabbinic law. So the whole process of doubt resolution involves legal rules, not risk assessment.
