"You shall safeguard and observe them, for they are your wisdom and your understanding in the eyes of the nations." (Devarim 4:6).
Why does the Torah suggest that the purpose of Torah observance is to be "wise in the eyes of the nations"? Isn't the purpose of our observance to fulfill HaShem's Will?
A person must attain wisdom of spiritual and worldly matters to fulfill the Torah. For instance, the Vilna Gaon teaches that a judge must be an expert in human nature, insightful of various personality types, and deceptive tactics of dishonest people. His sharpness of worldly wisdom coupled with his profound Torah knowledge gives him the capacity to render just rulings. What's more, our Sages assert that "derech eretz," human decency and etiquette, precedes the mastery of Torah.
The above verse reveals that the Torah, itself, is a complete resource of worldly wisdom. Through Torah study, a person can achieve a perfect knowledge of both religious and secular wisdom!
"You shall safeguard and observe them, for they are your wisdom and your understanding in the eyes of the nations." Meaning, the truth of the Torah contains the highest levels of worldly wisdom.
Torah scholarship is accomplished by mastery of both the spiritual and worldly realms of Torah knowledge. May we merit to absorb both aspects so that we fulfill the Torah in truth, holiness, and peace.
(Based on Ohr Rashaz of Alter of Kelm)