Question:

We're told that G‑d is unknowable, but also told to love G‑d. I don't get it: how can one love something that is "Unknowable"?

Answer:

Many men will tell you that after 25 years of marriage the woman they have lived with is still a great mystery to them. As my father-in-law put it in his typical engineer terminology, "By now, I have figured out which buttons to push. But I still have no idea how she works."

And yes, my father-in-law was madly in love with his wife after over 30 years at the time he said this.

What I'm getting at is that the same applies with G‑d. Yes, He is entirely unknowable—because He has no definition. But we do know how He relates to us, what He has created, and which buttons to press.

So that's where love comes in: We see that this infinite, unknowable G‑d—who has created a magnificent universe with endless stars and galaxies and even more creatures of unbelievable diversity, including us tiny creatures—actually desires a relationship with us. And He gives us the tools to build that relationship, a relationship so close and intimate that we can be with Him every moment of our day, in soul, mind and every limb of our body. If we would really think deeply into this, no doubt our hearts would melt.

(Rabbi Schneur Zalman of Liadi expands on this idea in chapter 46 of his Tanya--click here to read, or here to listen.)