Impermanent in their nature: That is, the same object which gives pleasure at one moment gives pain at another, and so on.

^37:15 Thus perfect sameness amidst the ills of life means full and unbroken consciousness of our oneness with the Immortal Self. Thus is immortality attained.

^38:16 Unreal: Real: The determination of the nature of the Real is the quest of all philosophy. Sri Krishna here states that a thing which never remains the same for any given period is unreal, and that the Real on the other hand is always the same. The whole of the phenomenal world, therefore, must be unreal, because in it no one state endures for even an infinitesimal division of time. And that which takes note of this incessant change, and is therefore itself changeless,--the Atman, Consciousness,--is the Real.

^38:17 That by which all this is pervaded, i.e. He that pervades all this as the Witness.

^39:18 Arjuna's grief which deters him from his duty of fighting against the Kauravas is born of ignorance as to the true nature of the Soul. Hence Sri Bhagavan's strong and repeated attempts to illumine him on the subject.

^40:19 Cf. Katha Up. I. ii. 19-20.

^40:20 This sloka refers in the sense of denial to the six kinds of modification inherent in matter: birth, subsistence, growth, transformation, decay, and death.

^41:21 How is he to slay?--referring to Arjuna. To cause another to slay--referring to Krishna's own part.

^42:22 As one only puts off the old, when one already possesses the new garment, so the embodied is already entering a new body in the act of leaving this. The Upanishad compares this to the movement of a leech, which has already established a new foothold before leaving the old.

^43:25 This Self is infinite and partless, so can be neither subject nor object of any action.

^44:26 Krishna here, for the sake of argument, takes up the materialistic supposition, and shows that even if the Self were impermanent, sorrow ought to be destroyed, since in that case there would be no hereafter, no sin, and no hell.

^44:27 This sloka concerns only those who are not yet free. So long as there is desire, birth and death are inevitable.

Therefore thou oughtest not to grieve: Since you cannot control the inevitable and preserve the bodies of your relations, work out your own Karma and go beyond both birth and death.

^45:28 Beings: In their relationships as sons and friends, who are mere combinations of material elements, correlated as causes and effects.

The idea here is that that which has no existence in the beginning and in the end, must be merely illusory in the interim, and should not therefore be allowed to have any influence upon the mind.