The final, 18th verse of the Isha Upanishad is an invocation of the divine Will to act in the life of the seeker, to overcome the pull of the egoistic consciousness and move the individual to a level of action that flows from the divine consciousness.
“O god Agni, knowing all things that are manifested, lead us by the good path to the felicity; remove from us the devious attraction of sin. To thee completest speech of submission we would dispose.”
Sri Aurobindo explains: “Sin, the conception of the Veda, from which this verse is taken bodily, is that which excites and hurries the faculties into deviation from the good path. There is a straight road or road of naturally increasing light and truth … leading over infinite levels and towards infinite vistas …, by which the law of our nature should normally take us towards our fulfilment. Sin compels it instead to travel with stumblings amid uneven and limited tracts and along crooking windings.”
In this sense, sin is not some subjective moralistic judgment, but an objective description of anything that gets in the way of the focus and dedication needed to achieve the shift from the human, ego-driven, desire-filled consciousness, to the the divine-centred adherence to the larger intention manifested through the development of the universe.
The individual needs to choose the higher, rather than the lower, options, and this involves submission to the divine Will in life rather than grasping at the fulfillment of desires as per the fragmented, divided and separate consciousness of the human standpoint.
“This is the change that happens when, the mental will approximating more and more to the divine, Agni burns out in us. it is that increasing knowledge and force which carries us finally into the straight or good path out of the crookedness. It is the divine Will, one with the divine knowledge, which leads us towards felicity, towards the state of Immortality. All that belongs to the deviations of the ego, all that obscures and drives or draws us into this or that false path with its false lures and stumblings are put away from us by it. These things fall away from the divinised Will and cease to find lodging in our consciousness. Therefore the sign of right action is the increasing and finally the complete submission of the individual to the divine Will which the illumination of Surya reveals in him. Although manifested in his consciousness, this Will is not individual. It is the will of the Purusha who is in all things and transcends them. It is the will of the Lord. Knowledge of the Lord as the One in the fully self-conscious being, submission to the Lord as the universal and transcendent in the fully self-conscious action, are the two keys of the divine gates, the gates of Immortality.”
“Thus the fourth movement indicates psychologically the double process of that attainment of Immortality which is the subject of the third movement, the state of bliss and truth within and the worlds of Light after death culminating in the identity of the self-luminous One. At the same time it particularises under the cover of Vedic symbols the process of that self-knowledge and identification with the Self and all its becomings which is the subject of the second movement and of that liberated action in the assertion of which the first culminates.”
Sri Aurobindo, The Upanishads, Isha Upanishad and analysis, pg. 23-24, 28 & 84-89