Thought, speech and action are entirely under a person’s control! On the other hand, changing one’s emotional instincts takes inordinate efforts and cannot be relied upon.
This is why G-d did not command Moses to spy on the Land of Israel. Moses sent spies on his own accord. Only before Joshua would take the Jews into the Holy Land, only then did G-d command that he send spies, and - only that they spy on the city of Jericho - not the entire country. Jericho was the key to unlocking Israel!
Why only Jericho and not the entire country?
Let’s first just understand that spying out Jewish territory implies, as every commandment in Torah is eternal, always inspecting one's resilience to follow Hashem's dictates. The Jew's soul is his personal Holy Land. Spying out the entire Jewish land means spying out one’s personality, temperments and behavior, to see if they remain in sync with divine demands. Conquering the land of the Cana’anites means to overhaul the entire terrain, both emotive and behavioral. But only Jericho could be relied on to deliver full control.
This is why G-d commanded that only Jericho be spied out, be investigated to see if one’s own “Jericho” subserves G-d’s wishes. Jericho, which in Hebrew comes from the word “odor”, relates to smell in that just as smell affects us but leaves no imprint, so too thought, speech and action do not reside within us.
That is to say, these 3 behaviors do NOT belong to the person. They come from an outside source directed for our use - but they do NOT belong to us as being part of our being, as do our emotive facets. To be sure - we need them also to exist, but they are not a fixture of our constitution; They are replaceable as such with other "ropes" also at our behest. We here have choice under full control. We can climb these ropes to draw ourselves higher. There are also other ropes, also of higher source, only these, were they to be used, can take the Jewish soul to lower than original depth.
For lack of a better illustration, think of the car. The car will not function unless gas “from the outside” is fed into it. Similarly, our “car souls” need to feed on thought, speech and action that we draw in, as the lung needs oxygen, from another divine source, to function.
These 3 behaviors interface with the soul to give the soul existence. Because they derive from a loftier source that the soul itself, they can raise the level of the soul to guarantee it attains a higher perch from which to experience future revelations of divinity in the world-to-come. Why else was the soul sent down here into the nethermost of all worlds - if not to improve its lot?
We spoke earlier of sources of divinity, how one is higher than the other (see here). (By the way, this conceptual construct of higher and lower is the spiritual analogue of the physical 3D world of space, because spiritually there is no “space”, only the “higher and lower” paradigm from which the physical phenomenon itself derives.)
This is why, in fact, a person can better himself. He has full control of his Jericho - his thoughts, speech and actions. Like a circus acrobat who swings from rope to rope to reach a higher landing, so too the soul, by grabbing on to the right 3 “garments” of the soul, can lift himself higher from where he initially stood. We speak here of the Divine Soul.
Of course, the corollary of this configuration is that the person can also climb steeply downwards. For just as he can choose to deflect bad thoughts and change bad speech and behavior in favor of good ones, so too, by choosing the 3 garments purveyed by the Bovine Soul, his Divine Soul can be dragged to a level far lower from where it originated.