Prayer is the “spiritual nourishment” of the soul

It is the soul of man that has first to be fed. And this spiritual nourishment prayer can best provide. 
(From a letter dated 8 December 1935 written on behalf of Shoghi Effendi to an individual believer, published in "Bahá'í News" 102 (August 1936), p. 3; The Compilation of Compilations, Vol. II, The Importance of Prayer, Meditation and the Devotional Attitude)

”The art of music is divine and effective. It is the food of the soul and spirit.”

What a wonderful meeting this is! These are the children of the Kingdom. The song we have just listened to was very beautiful in melody and words. The art of music is divine and effective. It is the food of the soul and spirit. Through the power and charm of music the spirit of man is uplifted. It has wonderful sway and effect in the hearts of children, for their hearts are pure, and melodies have great influence in them. The latent talents with which the hearts of these children are endowed will find expression through the medium of music. Therefore, you must exert yourselves to make them proficient; teach them to sing with excellence and effect. It is incumbent upon each child to know something of music, for without knowledge of this art the melodies of instrument and voice cannot be rightly enjoyed. Likewise, it is necessary that the schools teach it in order that the souls and hearts of the pupils may become vivified and exhilarated and their lives be brightened with enjoyment. 
(‘Abdu’l-Baha, from a talk at Children’s Reception Studio Hall in Washington, D.C., 24 April, 1912; ‘The Promulgation of Universal Peace: Talks Delivered by Abdu'l-Bahá during His Visit to the United States and Canada in 1912’)

Human voice “connects itself with the spirit” and “the spirit can be uplifted” by human voice

In the world of existence physical things have a connection with spiritual realities. One of these things is the voice, which connects itself with the spirit; and the spirit can be uplifted by this means -- for though it is a physical thing, it is one of the material, natural organizations -- therefore, it is effective. 
('Abdu'l-Bahá's, from an address quoted by to Mary L. Lucas in "A Brief Account of My Visit to Acca"; The Compilation of Compilations vol II) (To read the entire talk please visit Talks of ‘Abdu’l-Baha)

“As the soul of man is not the result of composition and does not come into being through the affinity of molecular elements, it is not subject to disintegration.”

We must first prove that there is no annihilation in creation. Annihilation is only the decomposition of elements. For example, all these things we see in existence are made up of elements; that is, single atoms have combined and have formed infinite patterns. Every combination produces an entity. For example, through the combination of certain elements this flower has come into existence. Its annihilation means only the decomposition of this combination, it does not mean the destruction of the individual atoms or principal elements because these remain and will not be destroyed. When we say that this flower is destroyed we mean that its combination is decomposed but the principal elements remain; only their combination is destroyed.

In the same way, man has come into existence as the result of the combination of certain elements. Although his death is the disintegration of these elements, the elements are not annihilated. Therefore, life consists of the combination of elements and death of their dissolution or transference from one state to another. The transference of the vegetable to the animal world is the death of the former. Draw your own conclusions from this. Similarly, the transference of man from this world of matter and the dissolution of his elements constitute human death. Thus, it should be known that for existence there is no death. At most there is a transfer from one state to another. As the soul of man is not the result of composition and does not come into being through the affinity of molecular elements, it is not subject to disintegration. If it were, then we would say the soul has died. But because it is not composed, therefore it cannot be decomposed. And it is clear that even the basic elements are not subject to decomposition as they are not a compound composition. No doubt remains regarding this matter. (‘Abdu’l-Baha, from a talk in Dublin, USA, August 7, 1912; Mahmud’s Diary)