What is the difference between Kamya and Nishkam service, and which is considered superior when studying spiritual texts?

According to the preface in chapter 0, spiritual texts, including Guru biographies, can be utilized with two different motivations. The first is 'Kamya,' which is desire-driven and aimed at gaining worldly prosperity or overcoming personal issues like distress and disease. The second is 'Nishkam,' which is a selfless approach undertaken for the purpose of liberation from the world or the cycle of birth and death. The text explicitly states that Nishkam Guru service, whether through writing a biography or any other form, will always be considered superior.