I knew there was something wrong with that translation the moment you posted it. I have a more accurate translation, with the context also given:
I-22: This highest mysticism, expounded in the Vedanta in a former age, should not be taught to one whose passions have not been subdued, nor to one who is not a worthy son, nor to an unworthy disciple.
VI-23: These truths, when taught, shine forth only in that high-souled one who has supreme devotion to God, and an equal degree of devotion to the spiritual teacher. They shine forth in that high-souled one only.
Translated by Swami Tyagisananda
Published by Sri Ramakrishna Math, Chennai
There is nothing new here. It had always been the tradition of the Vedic age to only teach Vedanta to a select few or chosen ones. Thus originally Vedanta was taught in the teacher-student tradition. Today, in the 21st century information age, such traditions are no longer relevent. Today anybody who has access to a computer, a library, a books store or a place conducting a course can learn Vedanta philosophy.
Get with the times.
I further read the Upanishad and I found that there is absolutely nothing being taught here that necessitates one MUST have a guru:
8: Placing the body in a straight posture, holding the chest, throat and head erect, and drawing the senses and the mind into the heart, the knowing one should cross over all the fearful currents by means of the raft of Brahman.
II-9: Controlling the senses with an effort, and regulating the activities in the body, one should breathe out through the nostrils when the vital activities become gentle. Then the knowing one, without being in the least distracted, should keep his hold on the mind as on the reins attached to restive horses.
II-10: One should perform one’s exercises in concentration, resorting to caves and such other pure places helpful to its practice – places where the ground is level without pebbles, and the scenery pleasing to the eyes; where there is no wind, dust, fire, dampness and disturbing noises.
I am not sure what period in time you are living in, but it clearly is not the 21st century. This knowledge today is public knowledge. It is studied and practiced openly and widely all across the world by hundreds of millions of people.
There was a time where the Vedas were not written down. Then they were. There was a time when only Brahmins could read the Vedas, today anybody can who either knows Sanskrit or has an English translation.
Rituals, traditions, customs and symbols change. It is the knowledge that is important here. If you don’t get that, I am sorry you are a simpleton who needs to develop a bit more before the real essence of Hinduism dawns on you.