רַבָּנָן אָמְרֵי, אָמַר הַקָּדוֹשׁ בָּרוּךְ הוּא לֹא לְרָעָתָם נָתַתִּי לָהֶם בְּרָכוֹת וּקְלָלוֹת, אֶלָּא לְהוֹדִיעָן אֵיזוֹ דֶּרֶךְ טוֹבָה שֶׁיִּבְחֲרוּ אוֹתָהּ, כְּדֵי שֶׁיִּטְלוּ שָׂכָר, מִנַּיִן, מִמַּה שֶּׁקָּרִינוּ בָּעִנְיָן (דברים יא, כו): רְאֵה אָנֹכִי נֹתֵן לִפְנֵיכֶם וגו'.
The Rabbis say... "HaShem says, he did not give for bad the curses and the blessings... rather to show the people which path o choose which is good, so they receive reward.. how do we know? We see this in the first verse of Re'eh...
Tangent to get to answer - We will now bring in a statement from Talmud to get a better idea of what's going on here..
מימות משה ועד רבי לא מצינו תורה וגדולה במקום אחד
From the days of Moses and until the days of Rabbi Yehuda HaNasi we do not find unparalleled greatness in Torah knowledge and unparalleled greatness in secular matters, including wealth and high political office, combined in one place, i.e., in a single individual.
Rabbi Abba said to Rabba bar Mari that there is an apparent contradiction in a verse. It is written: “All the disease that I placed in Egypt I shall not place upon you, for I am the Lord, your Healer” (Exodus 15:26). And since God does not place the disease upon the Jewish people, why is healing necessary?