Lately, I've been learning about the basic principles of Buddhism. It's very interesting to see how it correlates with spiritual principles and yet does not subscribe to traditional concepts of spirituality in the esoteric sense. Rather it describes spirituality in terms of the mind and the concept of "emptiness" (the idea of recognizing limitless potential while having form that is temporary. Same concept as our soul, having a temporary body containing a limitless soul that is released). Having a Christian background, I immediately saw the same high-level message in Buddhism as there is in the message of Christ, that we are enslaved by the "sins of the flesh" and that we must be "saved". In Buddhist terms, life is pure dukkha, or suffering, and this is due to cravings and desires of attachment (this is the same concept as sins of the flesh). In order to be freed from this perpetual Samsara (karmic reincarnation due to attachment), one must follow the path of enlightenment (righteousness in Christian terms). The Hindu religion also has the same principle, that of an ignorance of their true self due to sinful cravings and attachments to the flesh.
The aspect that I find missing in all of these religious principles is the gnostic knowledge of the esoteric. But I believe this was planned in order to train people who follow these religions towards a spiritual understanding through practice and experience in order to know the truth, rather than simple knowledge of the truth. The great messengers all taught what to do to be "saved" because it trains the mind (soul) to become "free" of ignorance to our true nature. If the messengers spoke the gnostic knowledge directly to people, the people would not have understood and would not have known how to be freed from their ignorance of self. This is one area that religions are in conflict with each other to proclaim the "only way" to be saved, because the true message is completely missed as they try to demonstrate how their message is the only way.
In Buddhism, without knowing what their deeper/hidden teachings are, due to the tradition of passing the more esoteric knowledge from master to disciple, on the surface the teachings will no more explain why we exist in the first place anymore than many other religions. To the religious, esoteric knowledge may appear to be devoid of a purpose other than gaining some scary mystical concepts or evil powers of ESP. But esoteric knowledge is what helps us in our spiritual development. Why does Buddhism promote meditation? Why does Christianity promote prayer? These are both the same acts that you do in order to "know yourself". Meditation is the means to realize your inner self through contemplation and observance, while prayer allows you to speak to that which is not seen ("God", which is the spiritual father of "you" in All That Is). The aspect of esoteric knowledge that really helps one to gain perspective on their true nature is the fact that you know why these religious actions work the way they do so that you can gauge progress. It goes beyond Buddhist goals of enlightened inner peace. It goes beyond Christian joy of salvation. Esoteric knowledge gives you the understanding of how to be what you want to be, beyond the limitations of the physical. To be able to perceive beyond the physical senses, to know that your thoughts become reality, to communicate through the connectedness with All That Is (one with the universe). These are the elementary goals of each of us and the different religions and philosophies, when practiced, provide the beginning steps towards the higher goal.
Why do you practice a religion? Why do you do what you do? What goal do you seek by your beliefs? These are all fundamental questions one must ask themselves if one wants to start to know who they are, and thus know what they are.
In my belief, samsara is not because of karmic debt nor is it the cause of the next life incarnation. Rather, the next life in samsara is driven by the need to experience all aspects of being. If one acted in a negative manner in a previous life, it did not cause your next life. The next life, if the previous life was a "bad" life due to "karma", is designed for you to experience and learn what the other side of your "bad" actions will be like. It is an educational tool, not a punishment. Suffering through attachment is the consequence of our learning process. We begin each life anew so that we can experience what we need to learn without any prejudice from our previous life. Then the outer ego (the part we associate with "I") will not expect anything, but rather experience everything as it happens and hopefully learn through it, eventually leading to a release from attachment of things and concepts (rigid beliefs are a form of attachment). This learning process adds to the overall experience of our inner ego (the soul), and thus produces a wiser personality. And this wisdom gained through multiple varying life experiences, carry forward into our future lives until we become whole (inner ego, aka soul, and outer ego, waking conscious mind, no longer think, and thus act, independently).
Buddhism has many very useful practical knowledge. It also has many of the esoteric knowledge available in a way that is relatable in human terms. But one must not take those teachings purely at face value anymore than the teachings of Jesus. Jesus spoke in parables so that those who are ready and able to seek the deeper truths through their examination of themselves will understand once they have experienced what Jesus was talking about. The same goes for the teachings of Buddha. He gave practical instructions on how to become enlightened so that when one becomes enlightened, they can start to find the meaning behind the teachings.