True strength is rarely found on a battlefield or measured by physical power. The ultimate test of power is the quiet, constant struggle a person wages within their own mind. The greatest victory one can achieve is mastering self-control and subduing natural urges.
The primary approach among commentators is that a patient person is far superior to a physical warrior because the warrior fights an external enemy, while the patient person must defeat an internal enemy, which is a much harder battle [אלשיך, מלבי״ם]. Winning a war or capturing a city is a single, isolated event, but mastering oneself requires constant, unyielding effort [ביאור שטיינזלץ]. Furthermore, a warrior shows strength through active movement and force, whereas true, deep strength is often proven through restraint and the choice to hold back from acting [מצודת דוד].
The dynamics of these two battles are fundamentally different. When a general sets out to conquer a city, all of his senses, limbs, and thoughts work together to help him succeed. However, when a person tries to hold back anger or suppress a desire, the mind must fight against its own body. The limbs naturally crave revenge or physical satisfaction. Overcoming this intense internal resistance without the body's cooperation is what makes self-control such a monumental achievement [עמנואל הרומי, אלשיך]. Additionally, capturing a city requires an army of helpers, but mastering the spirit is a deeply personal victory achieved entirely alone [אבן עזרא].
While some commentators view patience and ruling the spirit as two ways of describing the exact same control over anger [מצודת ציון, מצודת דוד], others see a clear progression between the two ideas. One approach suggests a difference between outward behavior and inward feelings: a patient person might successfully stop themselves from acting out in anger, even if they still hold a grudge inside. However, someone who truly rules their spirit reaches a much higher level, controlling their internal emotions so completely that thoughts of revenge never even enter their mind [מלבי״ם]. Another perspective is that the first stage deals strictly with overcoming anger, while the second stage is about defeating physical desires, which is the ultimate victory over the evil inclination [רש״י, רלב״ג, אלשיך].
The comparison to capturing a city is highly intentional. A human being is considered a miniature world, and the body is like a fortress city filled with the troops of the evil inclination. Whoever manages to rule their own nature effectively conquers an entire world. This is an infinitely greater achievement than taking over a physical city, which is only a tiny fraction of the earth [אלשיך, מלבי״ם, אמרי דעת]. Ultimately, a person who lacks the ability to rule their own desires is entirely unfit and unable to rule over anyone else [רלב״ג].