Obligatory Prayer:
We have [God has] commanded you to pray and fast from the beginning of maturity; this is ordained by God, your Lord and the Lord of your forefathers. He hath exempted from this those who are weak from illness or age, as a bounty from His Presence, and He is the Forgiving, the Generous.
(Baha’u’llah: The Kitab-i-Aqdas, pp. 22-23)

In truth, I say that obligatory prayer and fasting occupy an exalted station in the sight of God. It is, however, in a state of health that their virtue can be realized. In time of ill-health it is not permissible to observe these obligations; such hath been the bidding of the Lord, exalted be His glory, at all times.
(Baha’u’llah: Aqdas: Questions and Answers, p. 134)

The obligatory prayers are binding inasmuch as they are conducive to humility and submissiveness, to setting one’s face towards God and expressing devotion to Him. Through such prayer man holdeth communion with God, seeketh to draw near unto Him, converseth with the true Beloved of one’s heart, and attaineth spiritual stations.
(`Abdu’l-Baha: Prayer, Meditation, …, p. 232)

These daily obligatory prayers, together with a few other specific ones, such as the Healing Prayer, the Tablet of Ahmad, have been invested by Baha’u’llah with a special potency and significance, and should therefore be accepted as such and be recited by the believers with unquestioned faith and confidence, that through them they may enter into a much closer communion with God, and identify themselves more fully with His Laws and precepts.
(Shoghi Effendi: Directives of the Guardian, p. 60)

Concerning the directions given by Baha’u’llah for the recital of certain prayers, Shoghi Effendi wishes me to inform you that these regulations – which by the way are very few and simple – are of a great spiritual help to the individual believer, in that they help him to fully concentrate when praying and meditating. Their significance is thus purely spiritual.
(Shoghi Effendi: Prayer, Meditation, …, p. 237)

Fasting and obligatory prayer constitute the two pillars that sustain the revealed Law of God. Baha’u’llah in one of His Tablets affirms that He has revealed the laws of obligatory prayer and fasting so that through them the believers may draw nigh unto God.
(The Universal House of Justice: Aqdas: Notes, p. 176)

Communion with God:
The state of prayer is the best of conditions, for man is then associating with God. Prayer verily bestoweth life, particularly when offered in private and at times, such as midnight, when freed from daily cares.
(`Abdu’l-Baha: Selections … `Abdu’l-Baha, p. 202)

Thou hast asked the wisdom of prayer. Know thou that prayer is indispensable and obligatory, and man under no pretext whatsoever is excused from performing the prayer unless he be mentally unsound, or an insurmountable obstacle prevent him. The wisdom of prayer is this: That it causeth a connection between the servant and the True One, because in that state man with all heart and soul turneth his face towards His Highness the Almighty, seeking His association and desiring His love and compassion. The greatest happiness for a lover is to converse with his beloved, and the greatest gift for a seeker is to become familiar with the object of his longing; that is why with every soul who is attracted to the Kingdom of God, his greatest hope is to find an opportunity to entreat and supplicate before his Beloved, appeal for His mercy and grace and be immersed in the ocean of His utterance, goodness and generosity.
Besides all this, prayer and fasting is the cause of awakening and mindfulness and conducive to protection and preservation from tests….
(`Abdu’l-Baha: Baha’i World Faith, p. 368)

For the core of religious faith is that mystic feeling which unites Man with God. This state of spiritual communion can be brought about and maintained by means of meditation and prayer. And this is the reason why Baha’u’llah has so much stressed the importance of worship. It is not sufficient for a believer merely to accept and observe the teachings. He should, in addition, cultivate the sense of spirituality which he can acquire chiefly by means of prayer.
(Shoghi Effendi: Directives of the Guardian, p. 86)

Expression of Love and Gratitude:
In this day, to thank God for His bounties consisteth in possessing a radiant heart, and a soul open to the promptings of the spirit. This is the essence of thanksgiving.
As for offering thanks by speaking out or writing, although this is indeed acceptable, yet when compared with that other thanksgiving, it is only a semblance and unreal; for the essential thing is these intimations of the spirit, these emanations from the deep recess of the heart.
(`Abdu’l-Baha: Selections … `Abdu’l-Baha, p. 179)

In the highest prayer, men pray only for the love of God, not because they fear Him or hell, or hope for bounty or heaven…. When a man falls in love with a human being, it is impossible for him to keep from mentioning the name of his beloved. How much more difficult is it to keep from mentioning the Name of God when one has come to love Him…. The spiritual man finds no delight in anything save in commemoration of God.
(`Abdu’l-Baha: Prayer, Meditation, …, p. 236)

If one friend feels love for another, he will wish to say so. Though he knows that the friend is aware that he loves him, he will still wish to say so…. God knows the wishes of all hearts. But the impulse to prayer is a natural one, springing from man’s love to God.
Prayer need not be in words, but rather in thought and attitude. But if this love and this desire are lacking, it is useless to try to force them.
(`Abdu’l-Baha: Prayer, Meditation, …, p. 236)

Guidelines for Prayer:
The most acceptable prayer is the one offered with the utmost spirituality and radiance; its prolongation hath not been and is not beloved by God. The more detached and the purer the prayer, the more acceptable is it in the presence of God.
(The Bab: Selections from the Bab, p. 78)

The reason why privacy hath been enjoined in moments of devotion is this, that thou mayest give thy best attention to the remembrance of God, that thy heart may at all times be animated with His Spirit, and not be shut out as by a veil from thy Best Beloved.
(The Bab: Selections from the Bab, pp. 93-94)

It is seemly that the servant should, after each prayer, supplicate God to bestow mercy and forgiveness upon his parents. Thereupon God’s call will be raised: `Thousand upon thousand of what thou hast asked for thy parents shall be thy recompense!’ Blessed is he who remembereth his parents when communing with God.
(The Bab: Selections from the Bab, p. 94)

We must strive to attain to that condition by being separated from all things and from the people of the world and by turning to God alone. It will take some effort on the part of man to attain to that condition, but he must work for it, strive for it. We can attain to it by thinking and caring less for material things and more for the spiritual. The further we go from the one, the nearer we are to the other. The choice is ours.
Our spiritual perception, our inward sight must be opened, so that we can see the signs and traces of God’s spirit in everything. Everything can reflect to us the light of the Spirit.
(`Abdu’l-Baha: Prayer, Meditation, …, pp. 235-236)

Benefits:
Know thou, verily, it is becoming in a weak one to supplicate to the Strong One, and it behooveth a seeker of bounty to beseech the Glorious Bountiful One. When one supplicates to his Lord, turns to Him and seeks bounty from His Ocean, this supplication brings light to his heart, illumination to his sight, life to his soul and exaltation to his being.
During thy supplications to God and thy reciting, “Thy Name is my healing,” consider how thine heart is cheered, thy soul delighted by the spirit of the love of God, and thy mind attracted to the Kingdom of God! By these attractions one’s ability and capacity increase. When the vessel is enlarged the water increases, and when the thirst grows the bounty of the cloud becomes agreeable to the taste of man. This is the mystery of supplication and the wisdom of stating one’s wants.
(`Abdu’l-Baha: Prayer, Meditation, …, p. 235)

Thou hast asked about places of worship and the underlying reason therefor. The wisdom in raising up such buildings is that at a given hour, the people should know it is time to meet, and all should gather together, and, harmoniously attuned one to another, engage in prayer; with the result that out of this coming together, unity and affection shall grow and flourish in the human heart.
(`Abdu’l-Baha: Selections … `Abdu’l-Baha, pp. 94-95)

The believers, particularly the young ones, should therefore fully realize the necessity of praying. For prayer is absolutely indispensable to their inner spiritual development, and this, as already stated, is the very foundation and purpose of the religion of God.
(Shoghi Effendi: Directives of the Guardian, p. 87)

Answers to Prayers:
Spirit has influence; prayer has spiritual effect. Therefore, we pray, “O God! Heal this sick one!” Perchance God will answer. Does it matter who prays? God will answer the prayer of every servant if that prayer is urgent. His mercy is vast, illimitable. He answers the prayers of all His servants. He answers the prayer of this plant. The plant prays potentially, “O God! Send me rain!” God answers the prayer, and the plant grows. God will answer anyone. He answers prayers potentially. Before we were born into this world did we not pray, “O God! Give me a mother; give me two fountains of bright milk; purify the air for my breathing; grant me rest and comfort; prepare food for my sustenance and living”? Did we not pray potentially for these needed blessings before we were created? When we came into this world, did we not find our prayers answered? Did we not find mother, father, food, light, home and every other necessity and blessing, although we did not actually ask for them? Therefore, it is natural that God will give to us when we ask Him. His mercy is all-encircling.
But we ask for things which the divine wisdom does not desire for us, and there is no answer to our prayer. His wisdom does not sanction what we wish. We pray, “O God! Make me wealthy!” If this prayer were universally answered, human affairs would be at a standstill. There would be none left to work in the streets, none to till the soil, none to build, none to run the trains. Therefore, it is evident that it would not be well for us if all prayers were answered. The affairs of the world would be interfered with, energies crippled and progress hindered. But whatever we ask for which is in accord with divine wisdom, God will answer. Assuredly!
For instance, a very feeble patient may ask the doctor to give him food which would be positively dangerous to his life and condition. He may beg for roast meat. The doctor is kind and wise. He knows it would be dangerous to his patient so he refuses to allow it. The doctor is merciful; the patient, ignorant. Through the doctor’s kindness the patient recovers; his life is saved. Yet the patient may cry out that the doctor is unkind, not good, because he refuses to answer his pleading.
God is merciful. In His mercy He answers the prayers of all His servants when according to His supreme wisdom it is necessary.
(`Abdu’l-Baha: Promulgation of Universal Peace, pp. 246-247)

The prayers which were revealed to ask for healing apply both to physical and spiritual healing. Recite them, then, to heal both the soul and the body. If healing is right for the patient, it will certainly be granted; but for some ailing persons, healing would only be the cause of other ills, and therefore wisdom doth not permit an affirmative answer to the prayer.
(`Abdu’l-Baha: Selections … `Abdu’l-Baha, pp. 161-162)

…It is not sufficient to pray diligently for guidance, but this prayer must be followed by meditation as to the best methods of action and then action itself. Even if the action should not immediately produce results, or perhaps not be entirely correct, that does not make so much difference, because prayers can only be answered through action and if someone’s action is wrong, God can use that method of showing the pathway which is right.
(Shoghi Effendi: Lights of Guidance, p. 462)

Work is Worship:
This is worship: to serve mankind and to minister to the needs of the people. Service is prayer. A physician ministering to the sick, gently, tenderly, free from prejudice and believing in the solidarity of the human race, he is giving praise.
(`Abdu’l-Baha: Paris Talks, p. 177)

Work done in the spirit of service is the highest form of worship….
(`Abdu’l-Baha: Education, p. 313)