I want to change the second sentence like this
The reason why I want to become a nurse is that I want to provide a mental and physical stability to the patients. This is because it is important not only treat patients, but also it is necessary to make them recover quickly . So I will create a pleasant environment and provide mental stability and I will check the patient’s condition frequently so that the patients can recover as soon as possible.
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The reason why I want to become a nurse is that I want to provide a mental and physical stability to the patients. This is because it is important not only to treat patients, but also it is necessary to make them recover quickly . So I will create (or make) a pleasant environment and provide mental stability and I will check the patient’s condition frequently so that the patients can recover as soon as possible. (you can also use the word "quickly") .
this is already good 