MW13 writes: “While the pashtus of this certainly seems to imply like you said, I find it difficult to believe this statement was meant to be taken literally. After all, there are plenty of halachos that have nothing to do with menchlichkeit: avodah zora, emunah, etc. These are obviously fundamentals of Yiddishkeit, and yet they have nothing to do anybody but you and Hashem. Therefore, there must be more to the Torah then just bein adom li’chavaro. Remember, there are two luchos, and they are both equally important.”
Yes, that is a good point, but this is how I understand it. To deny the existence of the RBSH is terrible from the standpoint of menschlachkeit. He created the world, and gives us food and our health and our brains and worked very hard to supply us with our needs, and wants us just to say thank you, and have hakaras hatov. Just like if we turned our backs on our parents after all they did for us, and all their hard work, and staying up late when we were sick, and feeding us and driving us everywhere it would be the most despicable and ungrateful behavior there is.
In other words, the RBSH doesn’t want us to praise him because of his own ego trip, but he wants us to praise him because that is what makes a person a mensch, and the person will then use the same midos to show hakaras hatov to other people, as well, and this will cause ahavas habriyos and shalom in the entire world.
BTW, in the haftara of Yom Kippur it emphasizes that the purpose of the fast is to feel what hunger is like, and then understand what the aniyim feel, and to give them tzedaka. Halo paros lraev lachmecha vaniyim merudim tavi bayis….zeh tzom evchareihu. I don’t remember the exact words. (Heard from my Rav).