Updated: Jan 29
Before approaching if it is ok to be part both of a religion and a spiritual school at the same time, let's look into the specifics of each.
Religions’ specifics
Let's first all remember the basic functions of religion. Drawing a parallel with the usual school we all know, religions represent the 1st and 2nd class of spirituality. Thus, they teach a young soul some basic principles and commands such as: not to steal, not to lie, don’t be greedy, etc.
They also tell you that there is a God above all the time with his eyes on you, who looks like a grandfather with white hair and is always upset, and who slaps you at every mistake. So you would better live in fear of Him, otherwise it will be even worse … On top of that, there is a Hell around the corner waiting for you because of your sins, and you should be afraid of him too. So you fill yourself with fear of everything above you (God and the saints), as well as of everything under your feet (Hell) because we are all sinners, who can be without mistakes and perfect in these circumstances?

You are also told directly or indirectly that you are completely and hopelessly spiritually helpless, that you are a failure anyway, and that only religion X, Y or Z is your "salvation" in this world and especially in the other.
The offer of religions to compensate for all these sins and fears, many instilled in us by them actually, is that each has on offer an almighty prophet who somehow "saves" us, at least after death, this is of course if we believe in Him.
Religions also tell us that although we are so sinful and punished at every mistake by this God who’s angry by definition, He loves us in spite of our sins. In fact, they tell they do everything they can to guide us on the right path.
Some religions have also included more luxurious offers, such as if you do worthy deeds for that religion like for example you die bravely killing tens and hundreds of "enemies" even if innocent and unarmed people but of another faith, all sorts of lavish gifts are waiting for you in heavens, put aside for you.
Now, in order to move further up from the 2nd spiritual class, religions ask you to become their employee and not just a fan member like most people are, and as such you have to attend a school of their own to become a priest, a monk, a rabbi, an ulema, etc.
What seems to be ignored by all, including highly educated people, is that classical religions were conceived hundreds and thousands of years ago for the level of consciousness of that historical context, which was very different from today. This explains the master-slave relationship depicted in religions, which in fact copies the typical one of those times between the king and his subjects.
Religions actually have very little to do with true spirituality like connecting with your soul, with higher vibrations and entities, find out your destiny. Their main purpose is to ensure social stability, i.e. give a common story to each of their followers, so that millions and billions of people are able to collaborate and build huge constructs like cities, dams, armies, and nations that make a civilization.
The vast majority of souls now embodied on Earth are young souls, and many even lived in ancient times when those religions were relatively new and well-aligned with the historical context of that times. Therefore, these souls when adhering to the religion in which they spent many lives in the past do have a familiar feeling in the present. They feel at Home, have a sense of déjà vu, and feel safe since they share their faith with millions or even billions of others.
Spiritual schools’ specifics
However, in a true spiritual school, which I would liken to the 3rd and higher class in spirituality, the focus is on the Inside of the student and not on the Outside as it is in a typical religion. So the answers should no longer be sought like in a religion somewhere outside, but inside in the student's soul. A spiritual school (e.g. yoga, taichi, qigong) promotes a spiritual practice that is supposed to lead a student onto a more enlightened and higher awareness existence.
Of course, this endeavor is significantly more difficult and involves the identification and release from the student’s subconscious of the limiting beliefs he has adopted since childhood due to family, religion, education, society, media, etc. It’s hopeless to meditate if you do not seek to identify and release these beliefs that pull you down.
One of the main differences between a religion and a spiritual path is that religion provides common rituals that make followers feel together in a sense, not alone anymore, it gives everybody a sense of belonging to something bigger than them; this gives a feeling of soothing, being nurtured, more relaxed, more peace inside as being part of a larger community, and so on. Being alone triggers in most people stress, while being part of a community triggers relaxation.
In a spiritual school although you have a master and colleagues, ultimately you are alone on your evolution spiritual path, you know where it starts but you have no idea when it will lead you to. You will be pushed to look inside you, and acknowledge your fears, worries, and insecurities, and this is certainly stressful.
What does it mean to be part of both a religious and spiritual school?
There are still many spirituals who are with one foot in one religion and the other in a spiritual school, which is as if a student attends in parallel some 1st grade classes in the morning in a school, and in the afternoon other 3rd grade courses in another school. When moving from a religion to a spiritual school one needs some time for to transition to take place, and for that transitioning period he will be part of both. Problems start if he never lets go of his religious past, in which case the student risks getting confused in these circumstances, and no true long-term results can be obtained.
When a spiritual is under the pressure of two or more different sources of very different vibration like a religion on one side and a spiritual tradition on the other side, both his soul and body energy fields will suffer in time, since they will be literally "pulled" in different directions. Unfortunately, I saw many spirituals including so-called "gurus" and "masters" that, as you will see on their websites, claim to deliver at least 5 very different schools each, many mixed also with some religious influence. As a parallel, imagine you have 3 delicious cakes in front of you if eaten separately, but if you mix them together and then try to eat the mixture, there are very few chances you will get also something good to eat.
My advice is to keep things separate, and when following a spiritual tradition then invest yourself 100% in it. If after a reasonable time you feel it doesn't serve your spiritual progress anymore then move to another tradition you think suits you better, but abandon the former procedures altogether so as not to mix things up, and risk some backfire coming from mixing the two traditions.
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You can learn more by reading other posts in this spiritual site that are coming from a very different and fresh angle than spiritual mainstream, and based on a very long and personal experience and hands-on research, and not from books.
You might also consider a service like Psychic Readings in the Services section of this site from the ones listed here and get a spiritual diagnosis, or Healing limiting beliefs, or Compatibility for lovers, or attend my spiritual School of Body and Soul Ascension Mastery so to raise your body and soul awareness and reach into higher dimensions.