If we move according to the instructions of the Vedas, the perfect paths for our lives will be set. Otherwise, if we do not move in that way but act according to our whimsical ideas, our lives will be spoiled by confusion and will end in despair. Actually, because people at the present moment are not following the instructions of the Vedas, they are all confused.
His Divine Grace A. C. Bhaktivedanta Swami Prabhupada
Srimad-Bhagavatam 5.1.14, Purport

Just because mundane thoughts appear in the mind while we chant the holy name does not mean we should slacken our chanting. The useless thoughts will gradually disappear as the irrevocable fruits of chanting the holy names. Do not be in a hurry.
Srila Bhaktisiddhanta Sarasvati Thakura
Amrita Vani, “108 Essential Instructions”

There is only one God. If there were more than one God, this material world would not be organized so well. If there were many competing independent Gods, they would decree different conflicting material laws, each according to his own desire. . . . Looking at the material world, an intelligent and thoughtful person cannot fail to accept the idea that it was created according to the will of a single supreme person.
Srila Bhaktivinoda Thakura
Tattva-viveka 21, Commentary

“Hare Krishna, Hare Krishna, Krishna Krishna, Hare Hare/ Hare Rama, Hare Rama, Rama Rama, Hare Hare.” This verse is called the maha-mantra. It contains sixteen holy names of the Lord composed of thirty-two syllables. If you continually chant this maha-mantra, the seed of love of God will sprout in your heart. Then you will understand the goal of life and the process for achieving it.
Sri Chaitanya Mahaprabhu
Sri Chaitanya-bhagavata, Adi-khanda 14.145–147

Persons who try to reach the ultimate goal of life must expertly observe the Supreme Absolute Person and the living entity, who are one in quality in their relationship as part and whole. This is the ultimate understanding of life. There is no better truth than this.
Lord Anantadeva (Sankarshana)
Srimad-Bhagavatam 6.16.63

A person devoid of strength in devotional service cannot achieve the Supreme Soul, the Lord. Only one who is eager to practice devotional service through the process of chanting His holy names can enter the supreme abode of the Lord.
Mundaka Upanishad 3.2.4

Being completely cleansed of all material desires, the devotees are freed from all mental contamination. Thus they can always think of the Lord constantly and address Him very feelingly. The Supreme Personality of Godhead, knowing Himself to be controlled by His devotees, does not leave them for a second, just as the sky overhead never becomes invisible.
Sri Narada Muni
Srimad-Bhagavatam 4.31.20