A person must be conscious of the extreme sanctity of the letters of the Torah. Multiple worlds were created from each letter, and numerous secrets are hidden within them. The holy Zohar teaches us that a human being cannot grasp even a thousandth of these secrets and worlds. When the Creator first formed the letters, He created them as hidden light which cannot be comprehended...
The shapes of the letters as they appear in a kosher Torah scroll correspond spiritually to the upper worlds, as do all of the combinations of the alphabet and all of the numerological calculations which arise from them.
When the Creator first formed the letters, He created them as hidden light which cannot be comprehended. He then lowered them, one step at a time, until they were embodied in the form of the heavenly letters, which are spiritual lights. And when He gave them to us, He further embodied them in a physical form, on the model of the neshamah which cannot dwell in this world without a physical body to carry it.
Therefore, when learning Torah or praying, a person must pay great attention to the holiness of the letters. He must keep in mind that he is dealing with objects of great holiness, and make sure to act properly and with spiritual purity.
[from Pituchei Chotam, Parashat Pekudei, as anthologized in Peninei Avir Ya’akov.]