The whole world is engaged in sacrificing energy for advancement of learning, social upliftment, economic development and plans for total improvement of the human condition, but no one is interested in sacrificing for the sake of the Lord, as it is advised in the Bhagavad-gita. Therefore, there is no peace in the world. If men at all want peace in the world, they must practice sacrifice in the interest of the supreme proprietor and friend of all.
His Divine Grace A. C. Bhaktivedanta Swami Prabhupada
Srimad-Bhagavatam 2.6.28, Purport

The holy names of Krishna are the eternal Truth. All scriptures explain Krishna and nothing else. Krishna is the supreme controller, the creator, the maintainer, and the annihilator. Everyone, beginning from Lord Brahma and Lord Shiva, is His servant. The life of anyone who gives up the lotus feet of Krishna and explains things as separate from Him is useless as a result of his false statements. The philosophies in all scriptures headed by the agamas and Vedanta describe the wealth of devotion to the lotus feet of Krishna.
Sri Chaitanya Mahaprabhu
Sri Chaitanya- bhagavata, Madhya-khanda 1.148–151

An expert geologist can understand where there is gold and by various processes can extract it from the gold ore. Similarly, a spiritually advanced person can understand how the spiritual particle exists within the body, and thus by cultivating spiritual knowledge he can attain perfection in spiritual life. However, as one who is not expert cannot understand where there is gold, a foolish person who has not cultivated spiritual knowledge cannot understand how the spirit exists within the body.
Sri Prahlada Maharaja
Srimad-Bhagavatam 7.7.29

It is not logical to say that the Supreme Personality of Godhead does not have inconceivable potencies that can arrange for the Lord to possess mutually contradictory qualities, for no one has the power to understand the Lord completely. The Lord must have inconceivable potencies, for that is logical and it is also confirmed by the Vedic revelation. Therefore the idea that the Lord does not have such powers that can give Him mutually contradictory qualities is illogical and should be thrown far away.
Srila Jiva Goswami
Sri Paramatma-sandarbha, Anuccheda 58

One who follows the disciplic succession of acharyas knows things as they are.
Chandogya Upanishad 6.14.2

By worshiping the devotees of the Lord, all one’s desires will be fulfilled.
Mundaka Upanishad 3.1.10

The Lord’s transcendental form is the Absolute Truth, devoid of duality or of beginning, middle, or end. It is self-effulgent, eternal, and full of knowledge and bliss. Only through devotional service can one understand that form to be infallible.
Vasudeva Upanishad 6.5