Truth is the soul of religion. When Jesus came to earth he did not say, 'I have brought you a new religion never heard of by you or your ancestors.' He said he had not come to give a new law but to fulfill the law; in other words, 'I have come to continue giving you that which you have received before and have not understood.'
There are scriptures that mankind regards as religious scriptures, but imagine how little of that message a book can contain, and how much more must have been given that was never written in a book! If books were sufficient, then the book of Abraham or the earlier books that were kept as scriptures could be sufficient, but it was not the book. The messenger, whenever he came, came to give the life, the living spirit, the divine light that can shine like the sun during the day, so that no soul with the slightest spark of sincerity could ever doubt the truth and unity of the message. From http://wahiduddin.net/mv2/IX/IX_29.htm
The divine message has always been sent through those fitly endowed. For instance when wealth was esteemed the message was delivered by King Solomon; when beauty was worshipped, Joseph, the most handsome, gave the message; when music was regarded as celestial David gave his message in song. When there was curiosity about miracles Moses brought his message. When sacrifice was highly esteemed Abraham gave the message. When heredity was recognized, Christ gave his message as the Son of God. When democracy was necessary, Muhammad gave his message as the Servant of God, one like all and among all. ...
All Masters from the time of Adam till the time of Muhammad have been the one embodiment of the Master-ideal. When Jesus Christ is represented as saying, 'I am Alpha and Omega, the beginning and the end,' it is not meant that either the name or the visible person of Jesus Christ is the Alpha and Omega, but the Master-spirit within. It was this spirit which proclaimed this, moved by its realization of past, present, and future life, confident of its eternity. It is the same spirit which spoke through Krishna, saying, 'We appear on earth when Dharma is corrupted,' which was long before the coming of Christ. During his divine absorption Muhammad said, 'I existed even before this creation and shall remain after its assimilation.' In the holy traditions it is said, 'We have created thee of Our light and from thy light We have created the universe.' This is not said of the external person of Muhammad as known by this name. It refers to the spirit which spoke through all the blessed tongues and yet remained formless, nameless, birthless and deathless.
But the blind world, absorbed in its phenomena and impressed by a certain name and form, has clung to the name, forgetting the true being. It is this ignorance which has divided the children of men into so many divisions and separated one from the other by their own delusions: whereas in reality there exists one religion and one single Master, the only God. ... There has been one Teacher only, and He alone will be. All the names which the world has fought over, are His names, and all the physical forms that have won the adoration of the truth-seeking world are His forms.