Musar zu Jirmejahu 4:3

To what may this be compared? To one whose house is full of mud and mire. Even if he will bring into his house the finest golden vessels, it will not be beautified thereby. He must first remove the mud and mire and then bring in the vessels. And so is it in our instance. The Jew has been given the power through his cleaving to Torah and mitzvoth to root in his soul the holiness of the L-rd, as it is written (Bamidbar 35:34): "I, the L-rd, dwell in the midst of Israel." But when is this? When he does not allow the yetzer to reside there through his false ideas or filthy thoughts. And this is the intent of "And you shall not go astray after your hearts and after your eyes, after which you stray." (That is, [this will occur] only if you guard yourselves in the future against your straying). "so that you remember and do all of My mitzvoth, etc." That is, if you are careful not to go astray, as mentioned above, the great result will follow that through the doing of the mitzvoth you will be holy to the L-rd. (As the Men of the Great Assembly have formulated for the blessing over a mitzvah: "who sanctified us with His mitzvoth." ["so that" refers to "and you will be holy" (i.e., "so that, in remembering and doing My mitzvoth, you will be holy to your G-d")]. But if, G-d forbid, you do go astray, the mitzvoth will not avail for your becoming holy. And this is the prophet's intent in (Jeremiah 4:3): "Plow for yourselves a furrow and do not sow upon thorns." Happy is he who reflects upon this. It will be good for him in this world and in the next.