(condensed from Ein Ayah, Berachot 6:39)

Gemara:

Rav Zutra bar Tuvia said in the name of Rav: From where do you know that one makes blessings on good smells? It is from the pasuk, “All of the soul shall praise Hashem, may Hashem be praised” (Tehillim 150:6). What is it that the soul has benefit from and the body does not? It is from a good smell.

Ein Ayah: The reason the gemara has to find a source for the beracha on smell is that there is logic to say that the reason for berachot is to prevent one who is involved in animalistic enjoyment from sinking into animalistic lowliness. In that regard, the function of the beracha would be to remind him to attach to the physical benefit a spiritual benefit of recognizing Hashem’s role in creating with kindness all of mankind’s enjoyments.

If it were the case that the beracha was to prevent negative influences, then it would be necessary only for lower-level enjoyments such as eating and drinking. In contrast, delicate enjoyments such as smell, which by nature elevate the spirit and its strengths, would not require a beracha. That is why the gemara refers to smell as something from which the soul benefits and the body does not. In other words, it does not bring one to animalistic behavior. Yet the pasuk that refers to benefit of the soul says that this experience should also be the impetus to praise Hashem. The reason is that the purpose of a beracha is not merely to protect from negative but for the positive of elevating one to recognize his Maker. When one makes a beracha on a good smell, where there is no fear of the negative, he strengthens the realization that the beracha exists so that we should gain the positive.