The spiritual master is the external manifestation of God, who is situated in everyone’s heart as Supersoul. For one who is very serious about understanding the Supreme Personality of Godhead, Supersoul immediately renders assistance by directing him to a bona fide spiritual master. In this way the spiritual candidate is helped from within and without.
His Divine Grace A. C. Bhaktivedanta Swami Prabhupada
Easy Journey to Other Planets, Chapter 2

The Supreme Personality of Godhead, His different potencies, and His transcendental qualities all have inconceivable prowess. It is not possible to explain them fully. These three items attract the mind of a perfect student engaged in spiritual activities and overcome all other processes of spiritual activity.
Sri Chaitanya Mahaprabhu
Sri Chaitanya-charitamrita, Madhya 6.196–197

The Supreme Lord, the Supreme Personality of Godhead, is always fully satisfied in Himself. Therefore when something is offered to Him, the offering, by the Lord’s mercy, is for the benefit of the devotee, for the Lord does not need service from anyone. To give an example, if one’s face is decorated, the reflection of one’s face in a mirror is also seen to be decorated.
Sri Prahlada Maharaja
Srimad-Bhagavatam 7.9.11

Simply by material birth, human beings become attached within their minds to personal sense gratification, long duration of life, sense activities, bodily strength, sexual potency, and friends and family. Their minds are thus absorbed in that which defeats their actual self-interest.
Lord Sri Krishna
Srimad-Bhagavatam 11.21.24

Knowledge of the sacred scriptures destroys many doubts and enables us to understand things beyond our sense perception. One who does not see through the eyes of the scriptures is actually blind.
Canakya Pandita

Krishna will certainly deliver anyone who chants His names without offense or blasphemy.
Srila Vrindavana Dasa Thakura
Sri Chaitanya-Bhagavata, Madhyakhanda 9.246

Other than those who are inclined to the service of the Lord, no one can possibly achieve happiness from the Lord’s darshana [audience]. Since others consider the Supreme Lord an object of enjoyment, they lack a service attitude and are unable to achieve eternal happiness, which is the actual fruit of the Lord’s darshana.
Srila Bhaktisiddhanta Sarasvati Thakura
Commentary on Sri Chaitanya-Bhagavata, Madhya-khanda 10.255

I offer my respectful obeisances to Sri Krishna, whose form is eternal and full of knowledge and bliss, who is the rescuer from distress, who is understood by Vedanta, who is the supreme spiritual master, and who is the witness in everyone’s heart.
Gopala-tapani Upanishad 1.1