‘Abdu’l-Baha was asked if prayer was necessary since presumably God knows the wishes of all our hearts

‘Abdu'l-Baha said:

"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. If there is anyone that you love do you not seek an opportunity to speak with him, to speak lovingly with him, to bring him gifts, to write him letters? If you do not feel such a desire it would be that you did not love your friend. God knows the wishes of all hearts. But the impulse to pray is a natural one springing from man's love to God.

"If there be no love, if there be no pleasure or spiritual enjoyment in prayer, do not pray. Prayer should spring from love, from the desire of the person to commune with God. Just as the lover never ceases from wishing to communicate with the beloved so does the lover of God always wish for constant communication with the Deity.

"Prayer need not be in words, but in thought and attitude. But if this love and this desire are lacking it is useless to try to force them. Words without love mean nothing. If a person talks to you as an unpleasant duty with no love or pleasure in his meeting with you, do you wish to converse with him? Efforts should first be made to make attachment to God."

When asked how this attachment is to be made, how the love of God is to be obtained, since there are many people in the world who admit the existence of a Deity but without any emotion, ‘Abdu'l-Baha said:

"Knowledge is love. Study, listen to exhortations, think, try to understand the wisdom and greatness of God. The soil must be fertilized before the seed be sown." 

-' Abdu'l-Baha  (Words of ‘Abdu'l-Baha, from an article in The Fortnightly Review, June, 1911, by Miss E. S. Stevens; Star of the West, vol. 8, May 17, 1917)