Published in 1915, Asrar-i-Khudi (Secrets of the Self) was the first poetry book of Iqbal. Considered by many to be Iqbal's best book of poetry, it is concerned with the philosophy of religion. In a letter to the poet Ghulam Qadir Girami (d.1345/1927), Iqbal wrote that "the ideas behind the verses had never been expressed before either in the East or in the West." R.A. Nicholson, who translated the Asrar as The Secrets of the Self, says it caught the attention of young Muslims as soon as it was printed. Iqbal wrote this in Persian because he felt the language was well-suited for the expression of these ideas. In Asrar-e-Khudi, Iqbal has explained his philosophy of "Khudi," or "Self." Iqbal's use of term "Khudi" is synonymous with the word of "Rooh" as mentioned in the Quran. "Rooh" is that divine spark which is present in every human being and was present in Adam for which God ordered all of the angels to prostrate in front of Adam.

However, one has to make a great journey of transformation to realize that divine spark which Iqbal calls "Khudi". A similitude of this journey could be understood by the relationship of fragrance and seed. Every seed has the potential for fragrance within it. But to reach its fragrance the seed must go through all the different changes and stages. First breaking out of its shell. Then breaking the ground to come into the light developing roots at the same time. Then fighting against the elements to develop leaves and flowers. Finally reaching its pinnacle by attaining the fragrance that was hidden within it.

In the same way, to reach one's khudi or rooh, one needs to go through multiple stages which Iqbal himself went through, a spiritual path which he encourages others to travel. He notes that not all seeds reach the level of fragrance. Many die along the way, incomplete. In the same way, few people could climb this Mount Everest of spirituality—most get consumed along the way by materialism.