Guru Nanak, founder of the Sikh religion, dedicated his life to dissolving the man-made differences between Hindus and Muslims. By teaching a form of Advaita (non-dualism) he showed that Hinduism is not, in essence, incompatible with the basic tenet of the monotheistic religions - the unity of the Divine.
"That which is inside a person, the same is outside; nothing else exists; by divine prompting look upon all existence as one and undifferentiated;"
-Guru Granth Sahib
Guru Nanak and his companions once visited Mecca. An official was angered to discover them sleeping with their feet towards the Ka'ba, the sacred shrine. As they were dragged away, the Ka'ba appeared to move too.
Guru Nanak told him: "God does not live in one place. He lives everywhere."
The Sikh view is that spirit and matter are not antagonistic. Guru Nanak declared that the Spirit/Self is the only reality and matter is only a form of Spirit/Self.
"When I saw truly, I knew that all was primeval. Nanak (the person), the subtle (spirit) and the gross (material) are, in fact, identical."
Nanaka is an incarnation of Shri Adi Guru Dattatreya, the teacher/guru aspect of the Divine.
The Primordial Guru is associated with the ocean. As the ocean gradually wears away the rocks of the shore, so the teacher gradually wears away our ego and conditionings.