On Prayer and the Power of the Holy Spirit

Thanks to A for inspiring me to discover the following passage by Abdu'l-Bahá after reading her wisdom on prayer. I've bolded my favorite part. Only through the wisdom and guidance of the Holy Spirit, which we must seek through prayer and through our most earnest efforts to understand the wisdom of the divine and holy writings, can the greatest fruit be yielded.

As someone who is constantly struggling with questions like "why pray?" and "to what effect is prayer?" this passage also sheds some light.

"O thou handmaid of God! The heavenly glad tidings must be delivered with the utmost dignity and magnanimity. And until a soul ariseth with qualities which are essential for the bearer of these tidings, his words will take no effect.
O bondswoman of God! The human spirit possesseth wondrous powers, but it should be reinforced by the Holy Spirit. What thou hearest other than this is pure imagination. If, however, it be assisted by the bounty of the Holy Spirit, then will its strength be a thing to marvel at. Then will that human spirit uncover realities, and unravel mysteries. Turn thy heart fully to the Holy Spirit, and invite others to do the same; then shall ye witness wonderful results.
O handmaid of God! The stars in the sky do not exert any spiritual influence on this world of dust; but all the members and parts of the universe are very strongly linked together in that limitless space, and this connection produceth a reciprocity of material effects. Outside the bounty of the Holy Spirit, whatsoever thou hearest as to the effect of trances, or the mediums’ trumpets, conveying the singing voices of the dead, is imagination pure and simple. As to the bounty of the Holy Spirit, however, relate whatsoever thou wilt—it cannot be overstated; believe, therefore, whatsoever 161 thou hearest of this. But the persons referred to, the trumpet-people, are entirely shut out from this bounty and receive no portion thereof; their way is an illusion.
O handmaid of God! Prayers are granted through the universal Manifestations of God. Nevertheless, where the wish is to obtain material things, even where the heedless are concerned, if they supplicate, humbly imploring God’s help—even their prayer hath an effect.
O handmaid of God! Although the reality of Divinity is sanctified and boundless, the aims and needs of the creatures are restricted. God’s grace is like the rain that cometh down from heaven: the water is not bounded by the limitations of form, yet on whatever place it poureth down, it taketh on limitations—dimensions, appearance, shape—according to the characteristics of that place. In a square pool, the water, previously unconfined, becometh a square; in a six-sided pool it becometh a hexagon, in an eight-sided pool an octagon, and so forth. The rain itself hath no geometry, no limits, no form, but it taketh on one form or another, according to the restrictions of its vessel. In the same way, the Holy Essence of the Lord God is boundless, immeasurable, but His graces and splendours become finite in the creatures, because of their limitations, wherefore the prayers of given persons will receive favourable answers in certain cases. ...
O handmaid of God! 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.
O handmaid of God! The power of the Holy Spirit healeth both physical and spiritual ailments. ..."
-Abdu'l-Bahá