In view of all the above, it is readily seen that prayer is a general principle: the principle of becoming absorbed in the G-d-man relationship, to become G-d-centered as opposed to self-centered.
In this context we can understand why many codifiers do not regard daily prayer as a Biblical precept (de'orayta), as one of the 613 mitzvot, but merely as an ordinance of the sages (derabanan).
For the mitzvot, the 613 directives of the Torah, are the 'instruments,' the specific means, to effect the realization of the Torah's purpose. General, all-comprehensive principles are not part of a code of particular do's and don'ts.
Tefilah, as defined, is one such general principle. It is the very soul, the vital force, for all the mitzvot, for all the specific instruments.
Tefilah is thus compared to the spinal cord.
The 613 mitzvot of the Torah correspond to the 613 parts in the human body: the 248 commandments correspond to the 248 limbs, and the 365 prohibitions correspond to the 365 veins.
Now, the vertebrae of the spine are counted among the 248 limbs. The spinal cord itself, however, is not included among these. Just as the spinal cord in the vertebral column is the backbone supporting and upholding the body, so is prayer the spinal cord and backbone of the mitzvot. That is why it is not included among the specific commandments.
