Dear Rabbi Lazer,
How do you respond to someone who questions the relevancy of ancient Torah laws to modern day living, i.e. Laws of Kosher, The Sabbath, etc. All the best, You are doing great work, SL from Rockville, MD.
Nobody doubts that the design engineer of Harley-Davidson knows what's better for a motorcycle engine than anyone else does. If you own a Harley, you're ridiculous not to heed every single clause of the owner's manual. Why? The head engineer wrote that manual; he designed the bike, and knows what's best for it. So if he says, change oil and spark plugs every so-many miles, you'd better listen, or else you won't get maximum performance from your machine.
The same goes for the soul...
Hashem - The Almighty - designed the human soul. If you want maximum performance, you have to fulfill the recommendations of the owner's manual - that's the Torah. Since we are incapable of understanding the spiritual fiber of our own souls, we are also incapable of knowing what's good for the soul. Only the manufacturer - Hashem - knows what's good for the soul, and that's none other than the 613 ancient commandments mentioned in the Torah and elaborated upon in the Talmud and Shulchan Aruch (Code of Jewish Law).
Jews have a unique spiritual makeup - the neshama kedusha - that requires observance of 613 commandments. Otherwise, certain damages will be done to that highly delicate and ever so intricate soul. When a person fails to keep kosher for example, his or her soul acquires a coating of impurity that blocks out Divine light. A person who doesn't see or feel Divine light can forget about emuna and spirituality. Lack of spirituality manifests itself in bodily sicknesses, anger, anxiety, stress, and depression, just to name a few.
Yes, the laws are ancient, but so are our souls. The body lasts for 80 or 90 years if you're lucky, but the soul is eternal. We observe the ancient laws for the benefit of our souls, so that we can always be close to Hashem.
With blessings always, Lazer