Prologue: Fertility and freshness are certainly seen as desirous traits in the world. Even in our own religion, we ask Hashem "Chadeish Yameinu" to renew our days with vitality and freshness.
Which is why, when one examines the Berachos at the beginning of Bechukosai, one is struck by the contrast of a promise of continuity. Why does Hashem promise to bring things on a regular cycle. Why not allow the food to fall from heaven as was the case in the Midbar?
Rav Dovid Feinstein Shlita explains that Hashem created the world with rules of nature built in. Deviation from these rules, although sometimes necessary, is actually a deviation from Hashem's desire
which is the revelation of Hashem's control of this world through the rules of nature and his desire to be served from it based on those laws as well.
And, while in regard to the rules of nature as things don't change we tire of them, in regard to our relationship with Hashem, the opposite is true. That is, the more we devote ourselves to Hashem, the closer we come to him and the further from rejecting him we become. This, explains Rav Dovid, is not a contradiction. Rather, while Shlomo Hamelech declared Ein Chadash TACHAS HaShemesh – that there is nothing new under the sun, in regard to Torah study which is a world above the sun, there is always room for growth and the ability and desire to do it.
Thus, Hashem promises us – if we listen to him and follow his words – we will live in a world of nature and continually seek Hashem within it while growing closer and stronger to Him each step of the way.
Seeking (Medical) guidance
The Ramban (VaYikra 26:11) notes that when things are good and the Jewish nation is acting appropriately, God will allow their existence to supersede any rules of nature that stand in their way, allowing them to be well to the point where they will not even need doctors. In fact, Ramban adds that the Tzaddikim of previous generations, and even kings (Asa, Chizkiyahu) did not seek medical advice from medical professionals. Rather, they sought guidance from the prophets making the job of doctor in their days obsolete.
Many have approached these words of Ramban and declared that a God fearing Jew shouldn't seek the advice of a doctor. The Avnei Nezer quoted his father (old edition Choshen Mishpat 193 – left out of
current editions) who noted that a patient can override the orders of a doctor in regard to an order to eat forbidden foods for his health. The opinion of Ramban is utilized in order to sanction this practice
However, one must question whether these words are an accurate portrayal of the Ramban's intent. Did Ramban mean to tell us that the righteous ignore doctors?
Certainly, ignoring doctors is not within the purview of the Ramban's comments. For he himself notes (Toras HaAdam, Shaar Hasakana) that it is a Mitzva for a sick person to get well and seek medical attention. He includes this in the realm of Pikuach Nefesh. Moreover in his commentary to Sanhedrin (Milchamos, 74) Ramban notes that one who limits the desecration of Shabbos in order to save his life is liable to pay for that desecration with his life. Clearly, Ramban holds that one MUST go to lengths to seek medical attention. How then, are we to understand his comments in Parshas Bechukosai?
HaGaon HaRav Osher Weiss Shlita(Minchas Asher) noted that there is no contradiction. That Ramban's comments at the beginning of Bechukosai are really just assumptions for a generation where doctors will be phased out themselves as a result of the Jews living on a celestial sphere themselves. Until that point, one must go to doctors and live in the real world.
The Rashba (Shut HaRashba I:413) too, notes that going to a doctor is not antithetical to having faith. Rather, Rashba demands that we believe that God will send healing power through the hands of the
doctor. He adds that even the pious of pious must work with this framework and go to doctors.
Similarly, the Taz (Yoreh Deah 336:1) notes that real health comes from Hashem and through davening to him one experiences it. Since we are not worthy, we must seek natural manifestations and intermediaries in achieving his Refuah. Ergo, concludes the Taz, we are obligated to go to doctors. He even adds that this is the intent of Ramban in Bechukosai though, as previously noted, this seems to be the opposite of Ramban's comments there. Rav Osher explains that this must be a proof that unless one is part of the selected minority, he should go to the doctor.
Similarly, the Shach (Yoreh Deah, 228:5) notes that if one takes an oath to avoid Nevailah when he is a Choleh SheYeish Bo Sakana, that Shevua is actually not a valid one since he is already Mushba M"Har Sinai to keep Pikuach Nefesh.
In the end, Rav Osher Shlita maintains the obvious position, namely that a person must seek medical attention should the need arise. He adds that there is no dispute or doubt on this point.