617.  Loka is in the locative case, the final vowel indicating to the locative having been dropped for sandhi.  Niravishan is an adverb, equivalent to samyak-abhinivesam kurvan.  Tattadeva means “those and those” i.e., possessions, such as putradaradikam.  Kusalan is sarasaravivekanipunan.  Ubhayam is explained as karma-mukhin and sadyomuktim.  Bhisma here points out the superiority of the latter kind of Emancipation over the former; hence Vedic acts or rites must yield to that yoga which drills the mind and the understanding and enables them to transcend all earthly influences.

618.  The soul-state is the state of purity.  One falls away from it in consequence of worldly attachments.  One may recover it by yoga which aids one in liberating oneself from those attachments.

619.  The three words used here are vichara, viveka, and vitarka.  They are technical terms implying different stages of progress in yoga.  The commentator explains them at length.

620.  Everything that man has is the product of either exertion or destiny; of exertion, that is, as put forth in acts, and destiny as dependent on the acts of a past life or the will of the gods or pure chance.  Yoga felicity is unattainable through either of these two means.

621.  Sankhya is understood by the commentator as implying Vedanta-vichara.

622.  This verse is a triplet.  The commentator explains that Vedanta in the second line means Sankhya.  I think, this is said because of the agreement between the Vedanta and the Sankhya in this respect notwithstanding their difference in other respects.  The object of the verse is to say that according to the Sankhya, there is no necessity for silent recitation of mantras.  Mental meditation, without the utterance of particular words, may lead to Brahma.

623.  Both declare, as the commentator explains, that as long as one does not succeed in beholding one’s Soul, one may silently recite the Pranava or the original word Om.  When, however, one succeeds in beholding one’s Soul, then may one give up such recitation.

624.  There are two paths which one in this world may follow.  One is called Pravritti dharma and the other Nrivritti dharma.  The first is a course of actions; the second of abstention from actions.  The attributes indicated in 10 and 11 belong to the first course or path.  They are, therefore, called Pravartaka yajna or Sacrifice having its origin in Pravritti or action.

625. i.e., he should first cleanse his heart by observing the virtues above enumerated.

626.  Samadhi is that meditation in which the senses having been all withdrawn into the mind, the mind, as explained previously, is made to dwell on Brahma alone.

627.  The end declared by Bhishma in the previous section is the success of yoga, or freedom from decrepitude and death, or death at will, or absorption into Brahma, or independent, existence in a beatific condition.