Sant Mat or Surat Shabd Yoga drew its philosophical basis by taking the best from the Sufi (Islamic) and the Hindu traditions: especially the tradition of the Sant which already adopted certain methods developed further in the Sant Mat.
The tradition of the Sufis - Islamic mystics - who -essentially - believe in one God (monotheism) and the Human Pole who is the mouthpiece of God on earth and the instrument chosen by Him to convey the spiritual Light to the souls willing and ready for mystical union. Obviously Sufism consists of many other doctrinal details also, but these are the main concepts that Sant Mat took from Sufism.
From Hinduism was adopted the doctrine of karma (law of action and reaction, cause and effect) and the consequent doctrine of reincarnation, the concept of Samsara or becoming, the so-called Wheel of Life in which souls are forced to rotate continuously in an endless chain of births, deaths and rebirths. The force that compels souls to continuously rotate between births and deaths is the desire that is ever renewed and feeds itself. The desire for anything earthly which dominates the space of our consciousness at the time of the death of the body forces us to be reborn in this world to reap the fruits of our desires. This forces the souls to be born and die and then be born again on this earth until it becomes free from all earthly desires while yearning only for liberation from continuous rebirths in the absorption in God.
When we realize that earthly and temporal things cannot procure true happiness, that they are indeed often a cause of renewed suffering and we begin to wish for freedom from this thinly game as a drowning person wants the air, then the Life -which is the Great Master- comes to our rescue by creating in our existence situations for growth. But a human, by its own ability and strength, will never be able to divert his mind from every material object, from every sensual pleasure, from all attachments to turn his mind totally focused towards the Eternal Truth that is all together inconceivable. He needs help, rescue and the example of someone who has fully realized this Truth, this state of consciousness, and has been chosen by the Invisible Power to be His mouthpiece in the world of humans: His distributor Agent of the Divine Product (as I like to call it). This is the Human Pole chosen by God to serve as a beacon for humanity groping in the dark.
In every age, at any given historical moment, on this earth there are ever one or more authentic Masters who are able to realize the Eternal Truth and they play this enlightening role. It is not true that the Saints, Prophets, Messiahs, Avatars and Satgurus have appeared on the world stage during certain periods of time, and at any other time they are not there. The needs are always the same for humans, Mother Nature has always provided for her children to their every need, there is always food for the hungry and water for the thirsty. Also there are souls eager to solve the riddle of life, who feel a desperate need to return to their Origin.