This is what tzaddikim have taught us. A person can’t say, “What’s the big deal? After all, I am engaging in doing mitzvos. True, I have self-interest...but everyone has biases.” Says the Yosher Divrei Emes, “There is always a mixture of good and evil...but the question is how much is there of each, and what is your main motivation?”
If a person keeps Shabbos, but it is the time when he indulges in gashmiyus.... He has hasagos in ruchniyus, but it generally takes him a day or two to recover a semblance of eidelkeit from his Shabbos... On Shabbos, he doesn’t have his regular schedule, and he is so very tired... and so what should he do? תענוג בשבת שינה, sleep is considered oneg Shabbos... and oneg Shabbos is a very big thing. And when it comes to eating, it’s a time of overindulgence, R”l....
And his davening on Shabbos.... He tends to daven wherever it’s convenient, depending on when he awakes, sometimes here, sometimes there.... This person is growing more distant from the Ribbono shel Olam through Shabbos—Shabbos didn’t bring him closer.
A person may think: How is this possible? How can it be that by engaging in mitzvos, he can become more distant from Hashem? Says the Ramban in Kedoshim: If you’re not heading in the right direction, aiming to grow closer to Hashem, then you’re filled with ga’avah and ta’avah. And if one is busy indulging in ta’avah on Shabbos—instead of engaging in activities that will bring closeness to Hashem—it is a big problem. This is what the Ramban is teaching us: We must aim to get close to Hashem through תהיו קדושים, removing ourselves from ta’avah and ga’avah.
