I had composed a response to your query on the thread titled Offering and Seeking Instruction, but had not had a chance to finalize it or post it before I saw this thread.
Here you have added a reference to “spiritual relaxation.” I can think of multiple interpretations of this and so am even less confidant that I understand either the nature of your dilemma or the advice of your teacher. I support Louis in his desire for added clarification. I also think that the thread Jerry quoted leads to many possibilities that might be helpful to you or at least that might help you frame your dilemma more specifically.
Rather than let me previous draft rot away, I will go ahead and set it forth below:
Without seeing you in person, it is hard to offer advice. What I have to say may thus not apply at all. First, I am assuming that the type of Taijiquan you practice stems from Yang Zhenduo’s teachings or a system that is like his. In my opinion, there are substantial differences in methodology between systems that call themselves Taijiquan, or even Yang Style Taijiquan. In my opinion, what I have to say below applies to some, but not to others.
As I have posted before, I do not believe that all systems of Taijiquan actually follow the same method of “relaxation.” At present, I distinguish three different types that have some overlap, but which I believe are important not to confuse.
For many people, “relax” means to leave your muscles in a state of passivity. This is what one does when being massaged, for instance. If you do not “relax,” the action of the massage can cause pain. This is also what one does in a hot tub or Jacuzzi as you let everything go and try to avoid all sense of exertion.
Another type of “relaxation” is what Olympic athletes pursue. A coach might advise an Olympic swimmer to “relax” when trying to beat a world record. By this, he or she would not be advising the swimmer to leave muscles in a maximal state of passivity or to avoid exertion, but rather to avoid constriction in movement. Most people involved in competitive sports are familiar with this type of “relaxation.”
In my view, the Yangs’ emphasize a third aspect of “relaxation” that is related to the other two, but is still distinct. If you have been to one of their seminars, you may have seen them demonstrate “relaxation” in a fairly static position, by expanding their joints. I distinguish this type of relaxation from the first type, because on the surface it involves putting more "energy" into your posture, rather than less. You must consciously and palpably pull your joints open. I also distinguish this type of relaxation from the second type, because the process has clear application in a static position. In other words, the most important aspect of it is not specifically tied to ease of movement.
You alluded to the frustration and difficulty of trying to relax while having one’s mind preoccupied with fulfilling all the requirements of form. I would submit that if you follow the third method, you may discover that many of the requirements can only be fulfilled by “relaxing.”
Rather than trying to make your mind passive, you might find it easier to make it much more active, but in a different way than before. This may sound paradoxical, but I find it to be true.
If you have ever experimented with juggling, you will be familiar with the feeling of having so much to keep track of, that your mind cannot become stuck on anything, even for an instant. Flow becomes permanent. You might find the same sort of feeling in playing an instrument or balancing in a boat. Make your body feel like it is moving like the water in a waterbed. Every time one thing moves, it forces everything else to adjust. It is not that you choose to adjust everything else, but rather that your method of maintaining expansion and looseness in our body requires everything to adjust. If you try to view every movement and every sub-movement in isolation, you become overwhelmed and “all the balls” drop. If instead, you keep your attention “locked” on the flow, the movements lose their separateness. You feel how your movement keeps “all the balls” in the air, but you do not consciously relate any particular movement of your body to any particular result in the air.
At another level of analysis, too much mental activity involves “losing the forest in the trees.” If you try to keep too much detail in your mind, you inevitably become stiff and unable to flow. As an example, the Ten Essentials become at least nine too many.
One method I have found helpful that others have also mentioned from time to time is to concentrate very hard on one of the Ten Essentials to the exclusion of almost all else. The important aspect of this is to make sure to pay attention to the principle even when you think something else might be more important and you are tempted to let your mind wander. This is important because you are trying to break out of a mental limitation and understand how everything relates to everything else. Only by trying to concentrate on the particular principle even when it seems inconvenient, unnecessary, or even distracting can you sometimes understand why the principle truly is important. An example of this is concentrating on any of the upper body principles during the postures that require standing on one leg. Paradoxically, by concentrating on correctness in the upper body while one’s balance is most challenged, one can begin to feel how upper and lower physically relate to each other.
I hope this helps.