One should therefore understand that buddhi-yoga means to work in Kṛṣṇa consciousness, in the full bliss and knowledge of devotional service. One who works for the satisfaction of the Lord only, however difficult such work may be, is working under the principles of buddhi-yoga and finds himself always in transcendental bliss. By such transcendental engagement, one achieves all transcendental understanding automatically, by the grace of the Lord, and thus his liberation is complete in itself, without his making extraneous endeavors to acquire knowledge. There is much difference between work in Kṛṣṇa consciousness and work for fruitive results, especially in the matter of sense gratification for achieving results in terms of family or material happiness. Buddhi-yoga is therefore the transcendental quality of the work that we perform.
(Bhagavad-Gita----2:39----purport).

One who has actually come to understand one's constitutional position as an eternal servitor of the Lord gives up all engagements save working in Kṛṣṇa consciousness. As already explained, buddhi-yoga means transcendental loving service to the Lord. Such devotional service is the right course of action for the living entity. Only misers desire to enjoy the fruit of their own work just to be further entangled in material bondage. Except for work in Kṛṣṇa consciousness, all activities are abominable because they continually bind the worker to the cycle of birth and death. One should therefore never desire to be the cause of work. Everything should be done in Kṛṣṇa consciousness, for the satisfaction of Kṛṣṇa. Misers do not know how to utilize the assets of riches which they acquire by good fortune or by hard labor. One should spend all energies working in Kṛṣṇa consciousness, and that will make one's life successful. Like misers, unfortunate persons do not employ their human energy in the service of the Lord.
(Bhagavad-Gita----2:49----purport).

Lord Brahmā said: "The Supreme Personality of Godhead, being beyond birth and death, is eternal. He has no material qualities. Yet He is the ocean of unlimited auspicious qualities. He is subtler than the most subtle, He is invisible, and His form is inconceivable. He is worshipable for all the demigods. Innumerable universes exist within His form, and therefore He is never separated from these universes by time, space or circumstances. He is the chief and the pradhāna. Although He is the beginning, the middle and the end of the material creation, the idea of pantheism conceived by Māyāvādī philosophers has no validity. The Supreme Personality of Godhead controls the entire material manifestation through His subordinate agent, the external energy. Because of His inconceivable transcendental position, He is always the master of the material energy. The Supreme Personality of Godhead, in His various forms, is always present even within this material world, but the material qualities cannot touch Him. One can understand His position only by His instructions, as given in Bhagavad-gītā." As stated in Bhagavad-gītā (10.10), dadāmi buddhi-yogaṁ tam. Buddhi-yoga means bhakti-yoga. Only through the process of bhakti-yoga can one understand the Supreme Lord.
(Srimad Bhagavatam----8:6--summary).

Lord Krṣṇa, seeing the distressful condition of the living entities and forseeing their bleak future, spoke the scripture known as Bhagavad-gītā, which contains unequivocal instructions for mankind. These instructions are like the cooling showers of peace on the blazing forest fire of material existence. Ordinary human activities are quite different from the activities recommended in the Śrīmad Bhagavad-gītā; understanding this difference is essential for us. In our times we find many fruitive workers who claim to be karma-yogīs but in fact are seen to enjoy the fruits of their labor. What is needed is not this false karma-yoga but genuine buddhi-yoga, which Lord Kṛṣṇa several times explains in the Bhagavad-gītā. Buddhi-yoga means "devotion to the Supreme Lord." The Lord says in the Gītā (10.10), "To those who are constantly devoted to serving Me with love, I give the understanding by which they can come to Me."
(Renunciation through Wisdom).