Question by Inez Greeven during her pilgrimage in 1920:
"My friends came here, and they met you, and they visited
the Holy Places, but they were unaffected. When I came here I was
completely intoxicated with the greatness of the Cause. Why didn't they
become Baha'is?"
‘Abdu'l-Baha's answer:
“At the
gate of the garden, some stand and look within, but do not care to
enter. Others step inside, behold its beauty, but do not penetrate
far. Still others encircle this garden, inhaling the fragrance of the
flowers; and having enjoyed its full beauty, pass out again by the same
gate. But there are always some who enter, and becoming intoxicated
with the splendor of what they behold, remain for life to tend the garden."
If a man considers himself humble and lowly in the Cause of
God, he becomes glorified in all eyes. On the other hand, the moment he aspires
to personal greatness, he falls into disgrace and oblivion. 
When Mírzá Munír stated that one of the Arab travelers had
spoken to him about Mírzá Kheiralla's arrogance and heedlessness, 'Abdu'l-Bahá
replied:
One of the servants asked why man is not thankful when in
comfort.
It is natural for the heart and spirit to take pleasure and
enjoyment in all things that show forth symmetry, harmony, and perfection. For
instance: a beautiful house, a well-designed garden, a symmetrical line, a
graceful motion, a well written book, pleasing garments—in fact, all things
that have in themselves grace or beauty are pleasing to the heart and spirit… 
All pure things are acceptable. For example: water— pure—-is
acceptable; fresh air is most acceptable. As all pure things are acceptable and
pleasing, therefore a pure voice is most acceptable, and causes great
enjoyment.
…melodies, though they are material, are connected with the
spiritual, therefore, they produce a great effect. A certain kind of melody
makes the spirit happy, another kind makes it sad, another excites it to
action.