Apart from the spiritual requisites of a sanctified Bahá’í life, there are habits of thought that affect the unfoldment of the global Plan, and their development has to be encouraged at the level of culture. There are tendencies, as well, that need to be gradually overcome. Many of these tendencies are reinforced by approaches prevalent in society at large, which, not altogether unreasonably, enter into Bahá’í activity. The magnitude of the challenge facing the friends in this respect is not lost on us. They are called upon to become increasingly involved in the life of society, benefiting from its educational programmes, excelling in its trades and professions, learning to employ well its tools, and applying themselves to the advancement of its arts and sciences. At the same time, they are never to lose sight of the aim of the Faith to effect a transformation of society, remoulding its institutions and processes, on a sc ale never before witnessed. To this end, they must remain acutely aware of the inadequacies of current modes of thinking and doing-this, without feeling the least degree of superiority, without assuming an air of secrecy or aloofness, and without adopting an unnecessarily critical stance towards society.
(Universal House of Justice, 28 December 2010, to the Continental Board of Counsellors)

Every act ye meditate is as clear to Him as is that act when already accomplished.
(Bahá’u’lláh, Gleanings from the Writings of Bahá’u’lláh, p. 150)

For God has wished all good for His servants, and he who wishes the servants of God evil is against God; he has not obeyed the will and emulated the example of God; he has followed Satanic leadings and footprints. The attributes of God are love and mercy; the attribute of Satan is hate. Therefore, he who is merciful and kind to his fellowmen is manifesting the divine attribute, and he who is hating and hostile toward a fellow creature is satanic. God is absolute love, even as Jesus Christ has declared, and Satan is utter hatred. Wherever love is witnessed, know that there is a manifestation of God’s mercy; whenever you meet hatred and enmity, know that these are the evidences and attributes of Satan. The Prophets have appeared in this world with the mission that human souls may become the expressions of the Merciful, that they may be educated and developed, attain to love and amity and establish peace and agreement.
(‘Abdu’l-Bahá, The Promulgation of Universal Peace, p. 39)

For the highest thought of men, however deep their contemplation, can never hope to outsoar the limitations imposed upon Thy creation, nor ascend beyond the state of the contingent world, nor break the bounds irrevocably set for it by Thee. How can, then, a thing that hath been created by Thy will that overruleth the whole of creation, a thing that is itself a part of the contingent world, have the power to soar into the holy atmosphere of Thy knowledge, or reach unto the seat of Thy transcendent power?
(Bahá’u’lláh, Prayers and Meditations by Bahá’u’lláh, p. 327)

He must turn away from ideas which degrade the human soul, so that day by day and hour by hour he may advance upward and higher to spiritual perception of the continuity of the human reality.
(Shoghi Effendi, Lights of Guidance, p. 236)

He would advise her to turn her thoughts determinedly and intelligently—by that I mean unemotionally—to God, realising that He is forgiving, that in one moment He can, through His Blessed Mercy, take away our sense of failure and help us to do better in the future—if we sincerely wish to; to turn to Him in prayer and seek to draw closer to Him; and to accept His Will and submit her own desires and opinions to His Wish and plan for her.
(Shoghi Effendi, Lights of Guidance, p. 113)

I bear witness that the highest thoughts of all such as adore Thy unity, and the profoundest contemplations of all them that have recognized Thee, are but the product of what hath been generated through the movement of the Pen of Thy behest, and hath been begotten by Thy will.
(Bahá’u’lláh, Prayers and Meditations by Bahá’u’lláh, p. 149)

I might add that He does not believe any radiations of thought or healing, from any group, is going to bring peace. Prayer, no doubt, will help the world, but what it needs is to accept Bahá’u’lláh’s system so as to build up the World Order on a new foundation, a divine foundation.
(Shoghi Effendi, Lights of Guidance, p. 432)

In the early days of the Faith in Isfahan, when I began to study the Tablets and Writings of the Báb, and listen to the explanations of the friends, I found the proofs of His Revelation convincing and conclusive and the testimonies supremely sound and perfect. So I was assured in myself that this Cause was the Cause of God and the Manifestation of His Grandeur, the dawning of the Day-Star of Truth promised to be revealed by the Almighty. But when I was alone with no one to talk to, I was often overtaken with doubts. The idle fancies of my past life, and the whisperings of the evil one were tempting me... God knows how much I wept and how many nights I stayed awake till morning. There were days when I forgot to eat because I was so immersed in my thoughts. I tried by every means to relieve myself of these doubts. Several times I became steadfast in the Cause and believed, but later I would waver and become perplexed and dismayed.
(Adib Taherzadeh, Revelation of Bahá’u’lláh, v2, p. 197)

Man’s ignorance, his cruelty, his ungodliness, his selfishness, his insincerity and all his sins and shortcomings are tools of torture inflicting painful wounds upon the souls of the Chosen Ones of God, who have no alternative but to bear them in silence with resignation and submissiveness, as in the case of ‘Abdu’l-Bahá. One act of unfaithfulness—even a glance betraying the insincerity of the individual or an unworthy thought emanating from his mind—is painful torture to them. But they seldom reveal the shortcomings of men or dwell on their own pain and suffering.
(Adib Taherzadeh, The Child of the Covenant, p. 227)

Naturally, new spiritual thoughts and inclinations must also become manifest. If spirituality be not renewed, what fruits come from mere physical reformation? For instance, the body of man may improve, the quality of bone and sinew may advance, the hand may develop, other limbs and members may increase in excellence, but if the mind fails to develop, of what use is the rest? The important factor in human improvement is the mind. In the world of the mind there must needs be development and improvement. There must be reformation in the kingdom of the human spirit; otherwise, no result will be attained from betterment of the mere physical structure.
(‘Abdu’l-Bahá, The Promulgation of Universal Peace, p. 277)

Of course many wayward thoughts come involuntarily to the mind and these are merely a result of weakness and are not blameworthy unless they become fixed or even worse, are expressed in improper acts.
(Shoghi Effendi, Lights of Guidance, p. 364)

Often a man makes up his mind positively about a matter; for instance, he determines to undertake a journey. Then he thinks it over—that is, he consults his inner reality—and finally concludes that he will give up his journey. What has happened? Why did he abandon his original purpose? It is evident that he has consulted his inner reality, which expresses to him the disadvantages of such a journey; therefore, he defers to that reality and changes his original intention.
(‘Abdu’l-Bahá, The Promulgation of Universal Peace, p. 463)

Reflect that man’s power of thought consists of two kinds. One kind is true, when it agrees with a determined truth. Such conceptions find realization in the exterior world; such are accurate opinions, correct theories, scientific discoveries and inventions. The other kind of conceptions is made up of vain thoughts and useless ideas which yield neither fruit nor result, and which have no reality. No, they surge like the waves of the sea of imaginations, and they pass away like idle dreams.
(‘Abdu’l-Bahá, Some Answered Questions, p. 250)

Separate thyself from all thoughts, strip thyself from the unclean garment of attachment to this drossful (or earthly) world, arise for the service of thy Lord, the Clement, and be clothed with the robe of assurance (or certainty) so that thou mayest behold the hosts of confirmation from thy Lord arising from all sides.
(‘Abdu’l-Bahá, Tablets of ‘Abdu’l-Bahá v3, p. 650)

Some men and women glory in their exalted thoughts, but if these thoughts never reach the plane of action they remain useless: the power of thought is dependent on its manifestation in deeds.
(‘Abdu’l-Bahá, Paris Talks, p. 18)

The mind and the thought of man sometimes discover truths, and from this thought and discovery signs and results are produced. This thought has a foundation. But many things come to the mind of man which are like the waves of the sea of imaginations; they have no fruit, and no result comes from them.
(‘Abdu’l-Bahá, Some Answered Questions, p. 252)

The reality of man is his thought, not his material body.
(‘Abdu’l-Bahá, Paris Talks, p. 17)

The thought force and the animal force are partners. Although man is part of the animal creation, he possesses a power of thought superior to all other created beings. If a man’s thought is constantly aspiring towards heavenly subjects then does he become saintly; if on the other hand his thought does not soar, but is directed downwards to centre itself upon the things of this world, he grows more and more material until he arrives at a state little better than that of a mere animal.
(‘Abdu’l-Bahá, Paris Talks, p. 17-18)

Thoughts may be divided into two classes:
(1st) Thought that belongs to the world of thought alone.
(2nd) Thought that expresses itself in action.
(‘Abdu’l-Bahá, Paris Talks, p. 18)

What is inspiration? It is the influx of the human heart. But what are satanic promptings which afflict mankind? They are the influx of the heart also. How shall we differentiate between them?
(‘Abdu’l-Bahá, The Promulgation of Universal Peace, p. 22)

When we find a philosopher emphasizing the importance and grandeur of justice, and then encouraging a rapacious monarch in his oppression and tyranny, we quickly realize that he belongs to the first class: for he thinks heavenly thoughts and does not practise the corresponding heavenly virtues.
(‘Abdu’l-Bahá, Paris Talks, p. 18)

You should urge your fellow- Bahá’ís to … support you in a strong effort to suppress every critical thought and every harsh word, in order to let the spirit of Bahá’u’lláh flow into the entire community, and unite it in His love and in His service.
(Shoghi Effendi, Lights of Guidance, p. 91)