Disencumber yourselves of all attachment to this world and the vanities thereof. Beware that ye approach them not, inasmuch as they prompt you to walk after your own lusts and covetous desires, and hinder you from entering the straight and glorious Path.

Bahá’u’lláh, Gleanings from the Writings of Bahá’u’lláh, p. 275

Attachment to the earthly world, in relation to attachment to the spiritual world, is considered as a sin.

‘Abdu’l-Bahá, Some Answered Questions, p. 125

For attachment to the world has become the cause of the bondage of spirits, and this bondage is identical with sin.

‘Abdu’l-Bahá, Some Answered Questions, p. 123

For in the tavern of the mortal world the bile of the man of God is not removed. He will not rest a moment here and will not stain himself with the attachments of the world.

‘Abdu’l-Bahá, Tablets of ‘Abdu’l-Bahá v2, p. 380

God has given man a heart and the heart must have some attachment. We have proved that nothing is completely worthy of our heart's devotion save reality, for all else is destined to perish. Therefore the heart is never at rest and never finds real joy and happiness until it attaches itself to the eternal. How foolish the bird that builds its nest in a tree that may perish when it could build its nest in an ever-verdant garden of paradise.

‘Abdu’l-Bahá, Divine Philosophy, p. 136-137

It is because of this attachment that men have been deprived of essential spirituality and exalted position.

‘Abdu’l-Bahá, Some Answered Questions, p. 123

Man must attach himself to an infinite reality, so that his glory, his joy, and his progress may be infinite. Only the spirit is real; everything else is as shadow. All bodies are disintegrated in the end; only reality subsists. All physical perfections come to an end; but the divine virtues are infinite. How many kings have flourished in luxury and in a brief moment all has disappeared! Their glory and their honor are forgotten. Where are all these sovereigns now? But those who have been servants of the divine beauty are never forgotten. The result of their works is everywhere visible. What king is there of two thousand years ago whose kingdom has lived in the hearts? But those disciples who were devoted to God - poor people who had neither fortune nor position - are to-day trees bearing fruit. Their banner is raised higher every day.

‘Abdu’l-Bahá, Divine Philosophy, p. 137

Those who turned toward the Word of God and received the profusion of His bounties -- were saved from this attachment and sin, obtained everlasting life, were delivered from the chains of bondage, and attained to the world of liberty. They were freed from the vices of the human world, and were blessed by the virtues of the Kingdom.

‘Abdu’l-Bahá, Some Answered Questions, p. 124

You will find many of the wealthy exposed to dangers and troubled by difficulties, and in their last moments upon the bed of death there remains the regret that they must be separated from that to which their hearts are so attached. They come into this world naked, and they must go from it naked. All they possess they must leave behind and pass away solitary, alone. Often at the time of death their souls are filled with remorse; and worst of all, their hope in the mercy of God is less than ours.

‘Abdu’l-Bahá, The Promulgation of Universal Peace, p. 33

The gross materialism that engulfs the entire nation at the present hour; the attachment to worldly things that enshrouds the souls of men; the fears and anxieties that distract their minds; the pleasure and dissipations that fill their time, the prejudices and animosities that darken their outlook, the apathy and lethargy that paralyze their spiritual faculties--these are among the formidable obstacles that stand in the path of every would-be warrior in the service of Bahá’u’lláh, obstacles which he must battle against and surmount in his crusade for the redemption of his own countrymen.

Shoghi Effendi, Citadel of Faith, p. 148

The individual alone must assess its character, consult his conscience, prayerfully consider all its aspects, manfully struggle against the natural inertia that weighs him down in his effort to arise, shed, heroically and irrevocably, the trivial and superfluous attachments which hold him back, empty himself of every thought that may tend to obstruct his path, mix, in obedience to the counsels of the Author of His Faith, and in imitation of the One Who is its true Exemplar, with men and women, in all walks of life, seek to touch their hearts through the distinction which characterizes his thoughts, his words and his acts, and win them over, tactfully, lovingly, prayerfully and persistently, to the Faith he himself has espoused.

Shoghi Effendi, Citadel of Faith, p. 148

He further explains that one meaning of attachment to this world is attachment to those who have denied Him and repudiated His Cause.

Adib Taherzadeh, The Covenant of Bahá’u’lláh, p. 22-23

In a Tablet to one of the teachers of the Cause -- Mirza Abbas known as Qabil, a native of Abadih -- ‘Abdu’l-Bahá urged him to peruse the verses of The Hidden Words by day and night, and to supplicate God to enable him to carry out the exhortations of the Blessed Beauty. In the same Tablet He makes it clear that The Hidden Words is not merely to be read. Rather, it was given to the believers by Bahá’u’lláh to enable them to put into practice His counsels and commandments.

Adib Taherzadeh, The Revelation of Bahá’u’lláh v 1, p. 76

The possession of earthly goods is often misunderstood to be the only form of attachment. But this is not so. Man's pride in his accomplishments, his knowledge, his position, his popularity within society and, above all, his love for his own self are some of the barriers which come between him and God. To rid oneself of these attachments is not easy. It can be a painful process and may indeed prove to be a spiritual battle which lasts a lifetime. The Hidden Words can exert a potent influence in freeing man from the fetters of materialism and enabling him to win the battle against his own self.

Adib Taherzadeh, The Revelation of Bahá’u’lláh v 1, p. 76

To sever oneself from the Kingdom of Names may prove to be the most difficult task for a Bahá’í, and the struggle may indeed last a lifetime. If a man can only realize that his virtues are not intrinsically his own, but rather are manifestations of the attributes of God, then he is freed from the Kingdom of Names and becomes truly humble. Such a man will bestow divine perfections upon the world of humanity. This is the loftiest station that God has destined for man. To the extent that a believer succeeds in severing himself from these three forms of attachment, will he be fulfilling his part in the Covenant of God.

Adib Taherzadeh, The Covenant of Bahá’u’lláh, p. 28