The Holy Ohr HaChaim asks on this matter - The verse simply doesn't state what Moses was even asking of the Israelites! It just says this without specifying what this is..
And behold, it is taught in the Medrash -
The words of the above Midrash are puzzling. What is the intention here when the Medrash says, this Evil inclination remove from your heart. This seems to be warning us about this evil inclination that is already known to entice and trick us to do a thing, but we aren't being told what specific inclination we are being warned about!
Another question - What connection does this Medrash have to our opening verse and the above question of 'What thing is HaShem telling Moses to do'?
And there is to say with the Help of Heaven by opening with the words of the Holy Baal Shem Tov, may his merit rest upon us, who says a beautiful explanation on the below teaching from the sages -
And to explain, let us look at the following Talmud -
We have to understand, why is HaShem slaughtering the evil inclination? Wasn't this its purpose in its creation? To tempt humans in order that there be reward and accountability in this world? And that due to him there will be much greatness and preciousness in store for Israel in the world to come!? Seemingly the evil inclination was appointed to do this specifically!
So the Holy Baal Shem Tov, may his merit be upon us, teaches -
"The matter here is that the evil inclination agitates humans to chase after their temptations. He then sees that Israel acts in an elevated way, and they don't accept his words, so what does he do? He colors his words and makes himself appear to be promoting something that is a commandment or a good reality!
However, in truth, he was created to tempt humans to sin, and violate the will of The Creator, and NOT to appear as righteous, and a good reality that disguises/colors sins as good, and justifies them as commandments and good deeds. And because of this the evil inclination will be found guilty and punished in the future to come. And now we can explain the Talmud from above when it asks why is the slaughter liable? And the Tosfot then says we are talking about slaughters in general. Over here there is a hint referring to the evil inclination who slaughters the whole world and corrupts pure souls via seducing them into a world of sin of missing the point.
So - when the Talmud is wondering why is he liable, isn't this is what he was created for? We then see the answer is that he is liable for dying, as if to say that he is coming in the visage of the inclination of goodness, and he is really dying/coloring his face as if this reality he is pitching really is good.. and then this is why Shmuel (above in the Talmud) says his opinion that the evil inclination is liable due to taking a life. He is considered taking a life because he is successful in tripping up humanity in missing the point, and from this humanity gets disconnected from its pure soul. And for this he was NOT created. Therefor he is liable in regards to his mission here."
Until here are his Holy words.
Based on this we can better understand what Moshe was saying when he said 'This is the thing HaShem has commanded to do', and never explains what that thing really is, and then we have that Midrash that came in and said to remove the Yetzer Hara from our hearts. This is speaking specifically about the Yetzer Hara that tricks those into disguising a sin as a commandment, and on this specific scenario the verse says 'This is what יהוה has commanded that you do', 'to remove it from your hearts'.
And with this that was said we can explain what is said in the Hagada of Passover - "Lavan requested to uproot everything" - and how exactly did he try and do that? Based on what we said above it makes perfect sense. Lavan is comparable to the Evil Inclination in that he 'whitens' the sin and his face to make it look like a Mitzvah, and that is how he uproots everything, as not only is he causing man to sin by whitening a sin a mitzvah, and as the words of the Baal Shem Tov, ontop of all of that, he also removes the path of repentance from someone, since if a person knows that he actually did a sin, sooner or later he will come to repent for it, which is not the case if he didn't know in the first place that he committed a sin, and he rationalized within his brain that he actually did a Mitzvah, in which case he wont ever repent on it, and through this, Lavan uproots everything.
With this we can explain the teaching of the sages from the Talmud -
How is it possible that the inclination of someone who is fearing of the Heavens, and studies Torah day and night has an evil inclination that can be found within him thats much greater than a simple man? However, based on what we said before, it all makes sense. The intention when we say 'greater than his' means heavier than his to carry, as its hard and heavy, which means to say that when a simple man has his evil inclination take over him, tricks him simply to perform a sin, and has no need to whiten that sin to make it look like a mitzvah, since he is so simple, he will certainly be enticed and listen, and even if he resolved to not listen and fight it, he can still listen to the voice he knows that he can always sin, and then fix it, which is NOT the case with someone who is a great Torah scholar and has fear of Heaven, since for him the evil inclination has to whiten the sins to look like Mitzvahs in order for him to be listened to, and this inclination is very great and heavy, since a human is not aware he is sinning, and will never repent, and this is what it means that a greater man has a greater evil inclination.