This translation is by A. J. Aubrey who was in touch with Iqbal during the translation process, and also includes in the introduction an excerpt of the explanation given by the poet himself.
Iqbal's poetry is engaging and exquisite, but may seem dense. It includes a lot of concepts from Islamic mysticism which are difficult to understand for someone with no background in it.
Iqbal has this concept of "The Perfect Man" and his ideal is Blessed Prophet Muhammad. Here he is sharing "The Secrets" for how a "regular man" (or woman! for that matter) can keep becoming their "perfect self."
I say "keep becoming" because Iqbal believes this perfection is unattainable. As a person starts this journey, they get closer and closer to this perfection, but never really reach it. To him, a man is perfected (or comes in close proximity to perfection) by striving on this path, and it's not so much about the destination itself. In fact, it can be said that he reversed the question from "What level have you reached?" to "For how long have you traveled?" as a marker for measuring progress.
This shows his humility in acknowledging human limitations, imperfections, deficiencies, etc., it also shows his inclination towards individualism -- no two people can compare their journey as progress is not measured by some static goal. It also shows how much he values effort -- the journey never ends, regardless of what "level" you are on, there is always room for improvement.
Most of Iqbal's mystic concepts are taken from Rumi's work, whom he refers to as his spiritual guide, and whose Masnavi he has called the Persian Qur'an.
He does disagree with Rumi, however, in considering self effacement (explained below) as the highest goal to which one should aspire. This itself shows a mature understanding on Iqbal’s part, considering this was still written towards the earlier period of his work, that is to respectfully disagree on a single point without feeling the need to reject the person, or the system, in its entirety.
Self effacement or "fanaa" is a concept derived from the Qur'anic concept of "taqwa" or God-consciousness; that a person is so conscious of God that they never intentionally do anything that would displease Him. This is contrasted in Qur'an with "ghaflah" or heedlessness; that a person is so forgetful of God that they don't even realize, or care, that what they are doing is displeasing to God.
The mystics asked how much should a person be conscious of God? Most of the persian mystics (like Rumi) said one should be so much conscious of God that they completely forget and erase everything and everyone else from their consciousness, even their own identity (in your mind, you stop viewing yourself as a Self). And only remain aware of God.
We all experience this effacement in moments when we are so absorbed in our work or a thought that we completely forget ourselves, even if for very brief moments. But the hint of the experience is enough to understand the concept, right?
Iqbal’s main issue with effacement is getting absolved in God. Instead he argues that every creation is individual and should become more and more individual in order to reach perfection. Rather than getting absolved in God, one should absorb God in oneself because only through donning these attributes, such as mercy, peace etc., can a person reach wholesomeness in individuality. Iqbal's concept is rooted in this idea that at the core everyone is "pure" and the corruption is not a part of the Self, but is a result of corrupt actions. So the secret of the self is to bring it back to its original design by Self presevation, and not self effacement.
Although this book is said to have acted as a jail-break at a time of intellectual-enslavement, it does present a nice blend of both mysticism and intellectualism.