Excerpts from Kirpal Singh's book Godman. Unabridged Source.

From Chapter 5: Unless God comes down in the garb of man, we cannot know the Unknowable. The teachings of scriptures remain scaled to us under the heavy weight of ancient and archaic verbiage, unless a Master Soul who has actual experience of the Science of the Spirit explains to us the truth of these scriptures.

Even the apparently simple teachings of the late Masters fail to yield the right import unless some living adept in the line tells us their true significance, and makes us experience the same experiences mentioned in the scriptures.

By transmitting his own life impulse, he enlivens the spirit lying helplessly shriveled in the body under the dead weight of mind and matter. Like a clever guide, he, in an inimitable way of his own, quietly gives her a new lead.

Next, he lays bare to the spirit's view new heavens full of wondrous sights, charters her a plane (Shabd) and pilots her Godward himself. From day to day the spirit is wheeled around sharp corners, touches new spots, experiences unknown thrills, and enjoys exhilarating experiences too subtle to be described

From Chapter 7: TODAY a person who is ill cannot have the benefit of medical advice from Dhanwantri (the progenitor of medical science), nor can a litigant ask Solomon to decide his case, nor can a lady marry Adonis and bring forth children.

Similarly, Saints who appeared in the past from time to time and conferred spiritual benefit on those who came into contact with them, cannot do anything for the present generation. Each had his commission, and on completing it, entrusted the work of regeneration to his successor. Man can learn only from man, and God works His ways through living Saints.

Some people think that past Mahatmas continue to live in spiritual regions and can even now confer spiritual benefit on the aspirants. Let us see how this holds good in the light of reason:

1. Each Saint has his mission in life and comes with a definite instrument of instruction. As soon as he completes his job, he retires from this world (physical plane) and goes back into the Spiritual Ocean from which he sprang, leaving the work of further reorientation to his successor.
2. Again, in accordance with the Law of Nature, even if the predecessor has had to do something for his followers, he does it through the living successor to whom he entrusted the work on retirement; and only the latter as a brother-in-faith or Gur-bhai may help and guide his brethren on the physical plane.
3. It is only when we are able to leave the physical plane at will or at the time of death that we can contact the Master who initiated us if he has left the body. Even while living on this earth his resplendent and luminous form never comes down from the Gaggan (astral heaven), for he always awaits human spirits at the threshold of the materio-spiritual regions.
4. Again, in the hope and belief that the ancient Saints and sages can even now help us, we begin to attach great importance to ill-shaped and ill-formed currents and undercurrents of thought and feelings, and try to work on the suggestions of our own subconscious mind, little understanding its true import, and taking for granted that the impressions are from this or that past Master. These manifestations may even have been stirred up by some agency other than that of our Isht Dev, or the past Master of our choice. This cannot be seen in its proper perspective unless one is first gifted with inner vision (Divya Drishti), which can successfully penetrate  through the veil of mind and matter and see clearly and judge correctly the nature of the ill-conceived inner urges, as they swim up indistinctly to the mental surface.
5. Alongside the above, we cannot possibly understand the working of a prophet whom we have never met and seen with our eyes, nor have we the means to verify  his modus operandi. In these circumstances, we can easily be deluded by any wandering spirit or will-of-the-wisp, or may even fall easy prey to the Negative Power, with its diverse ways of enticing untrained souls.
6. If, for instance, it may for the moment be admitted that the ancient sages can still lead us on the spiritual path and the present Master is not needed for spiritual instructions, then the very idea of having a Guru at any time in the past or present is at once eliminated, for God can directly teach man easily without any prophet or Messiah.
7. The very fact that a sage or seer appeared at one time or another and helped people Godward is in itself proof, conclusive and positive, even in this age, that there is need of such a Godman; for without him one cannot know of God or move Godward.
8. God by Himself can teach man only by becoming man, for man alone can teach man. He has perforce to put on the garb of man-call him what you will: a Sadh, Sant, prophet, Messiah or Rasul. Like attracts like is an incontrovertible dictum.

The fact is that a person who denies and derides the necessity of a Master in Truth and yet wants to learn Truth all by himself does not in fact want it.

His case is just like that of a man who prefers to dig a well for himself rather than quench his thirst at a spring of cool and refreshing water nearby, with a waterman ready to serve him

The need of a Guru or Master is absolute, and there can be no exception to the rule. Suppose, for instance, a person wants to have a joy-ride in the air. No one will allow him to enter a plane by himself. Even if he enters it surreptitiously, he will find the machinery locked. If somehow or other he overcomes this obstacle, he will not know how to handle the various parts of the machine. Should he dabble with it and the plane starts, he cannot take it up for want of necessary training, nor can he bring it down, nor steer it correctly. The result, sooner or later, will be a crash and loss of life. The mechanism of the human body is much more complicated and delicate than that of any machine; therefore the need of a spiritual adept is all the greater, both for success in the practical process of self-analysis and also for the approach to God Himself and the understanding of the working of the divine Will.

The spirit imprisoned in the body cannot per se separate itself from it. With its seat above the focus of the eyes, it permeates the entire system, and the two are indissolubly intertwined with each other. Should it somehow or other find itself freed momentarily and collected and gathered up at its center, it cannot enter the airliner of Shabd. If it may find a way in, it does not know where to go, how to go, and how to return.

But if the master pilot (the Sant Satguru) could be there to take the spirit along with him, and the two could enter the plane and take a few joyful rides together in the spiritual realm, the spirit could also learn how to handle the heavenly liner, and to repeat the spiritual, experiments

One well-versed in the mechanism of the human body (which is composed of three coverings: physical, mental, and causal, plus the living sentient entity underneath), a habitual traveler to the heavenly regions, day in and day out, can initiate a spirit into the mysteries of   spiritual knowledge, and by a practical demonstration show her a "Way Out."

By actual guidance and help, the Master himself steers her safely from plane to plane, and explains on the way the dangerous signals and points, sharp turns and twists, and the dangers of the unknown and untrodden spiritual realms. Blessed indeed is the spirit that comes across such an adept in the science and art of Spirituality.

From Chapter 14: A Master Soul is the greatest benefactor on earth. His work is of the highest order. He comes to liberate the souls from the vast prison-house of mind and matter, so that he may take the exiles back to their glorious home and restore them to their rich heritage. A kindly soul may direct the prison warden to provide delicious food for the prisoners under his charge. Another may grant the boon of delicacies to them. A third may order for them good clothing and lodging and so on. Each of them no doubt may do something to ameliorate their lot for the time being.

But if someone were to throw open the prison gate and ask them to escape the squalor and misery of the jail, his work would naturally be counted as one far excelling the works of others.

This is exactly the nature of the work of a Master Soul. He reveals to us the Lost Kingdom, and restores us to Paradise from which Adam and, through him, his progeny were driven out for the original disobedience to God's Commandment.

Man had an ignoble fall from the Garden of Eden, and none could restore him to the good grace of the Father and bring about reconciliation except the Son of Man. He takes upon himself the vicarious responsibility for the sins of man, purifies him of all ignominy and by a transfusion of his own Life Impulse makes him arise into cosmic awareness and gain everlasting life.

But if someone were to throw open the prison gate and ask them to escape the squalor and misery of the jail, his work would naturally be counted as one far excelling the works of others.

This is exactly the nature of the work of a Master Soul. He reveals to us the Lost Kingdom, and restores us to Paradise from which Adam and, through him, his progeny were driven out for the original disobedience to God's Commandment.

Man had an ignoble fall from the Garden of Eden, and none could restore him to the good grace of the Father and bring about reconciliation except the Son of Man. He takes upon himself the vicarious responsibility for the sins of man, purifies him of all ignominy and by a transfusion of his own Life Impulse makes him arise into cosmic awareness and gain everlasting life.

From Chapter 16: The process of home-going and progress on the path is entirely at his discretion, and he is the sole judge for the time and measure of each step Godward.

From the time the spirit crosses over to the astral plane and comes face to face with the self-luminous form of the Master, the jiva has nothing more to do and strive for. It is the Master's job henceforth.

Excerpts from Kirpal Singh's book Godman. Unabridged Source.