Bhakti movement in Medieval India is responsible for the many rites and rituals associated with the worship of God by Hindus, Muslims and Sikhs of Indian subcontinent. For example, Kirtan at a Hindu Temple, Qawalli at a Dargah (by Muslims), and singing of Gurbani at a Gurdwara are all derived from the Bhakti movement of medieval India (800-1700). "The word bhakti is derived from Bhakta meaning to serve, honour, revere, love and adore. In the religious idiom, it is attachment or fervent devotion to God and is defined as "that particular affection which is generated by the knowledge of the attributes of the Adorable One." The concept is traceable to the Vedas where its intimations are audible in the hymns addressed to deities such as Varuna, Savitra and Usha. However, the word bhakti does not occur there. The word occurs for the first time in the Upanisads where it appears with the co-doctrines of grace and self surrender." (Heritage of the Sikhs, Harbans Singh) Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/historical-events/27581-the-bhakti-movement-800-1700-a.html
Bhakti movement spawned into several different movments all across North and South India. In North India, Bhakti movement is nonethless not differentiable by a Sufi movement of Shia Muslims of Chisti fame. People of Muslim faith adopted it as a Sufis while Hindus as Vaisanava Bhakti. Sufi saints of Chisti order produced first punjabi sufi saint named Baba Sheikh Farid Shakarganj, who paved the way for the punjabi nationalism as well as brought peace among Hindus and Muslims. " In the north the cult was essentially Vaisnava-based, but instead of being focussed on Visnu, it chose to focus itself on Vishnu's human incarnations, Rama and Krisna, the respective avatars or deities central to the two epics Ramayana and Mahabharata. For bhakti now Visnu's incarnations ( Rama and Krisna) were the direct objects of devotion. Adoration of the devotees was focussed on them in association with their respective consorts: Slta with Rama; and Rukmini, his wedded wife, or Radha, his Gopika companion, with Krisna. Images of these deities and their consorts installed in temples were worshipped. The path of bhakti was not directly accessible to the lower castes; for them the path of prapatti (unquestioned self-surrender) was prescribed. Singing of Bhajans and dancing formed an important part of this worship. The dancers were deva-dasis (female slaves of the deity) inside the temple, but nagar-badhus (public wives) outside. Apart frorn being overwhelmingly ritualistic, the worship tended to be intensely emotional." (Heritage of the Sikhs, Sardar Harbans Singh) Reference:: Sikh Philosophy Network http://www.sikhphilosophy.net/showthread.php?t=27581
Followers of Bhakti movement in twelveth and thirteenth Century included the saints such as Bhagat Namdev, and Saint Kabir das who insisted on the devotional singing of praises of lord through their own compositions. Since Bhakti movement was started before Guru Nanak, many historians have implied that Sikhism as started by Guru Nanak was nothing more then a Bhakti movement of Punjab. This is totally wrong and is against the basic Sikh virtues of equality of humans and worship of one God. There is no doubt that Sikh Gurus adopted the singing of devotional songs in praise of lord from Bhakti but there is a huge difference between Bhakti, sufiism and Sikhism. Although Sufi and Bhakti saints are revered and recognized by Guru Granth Sahib but they do not form the main basis of Sikhism. Sikhism lay emphasis on equality of Male and Female, good work ethic and as well as leading a good virtuous married life, which is Maya according to many Bhakti and sufi saints. Thus although Sikhs revere saints such as Bhagat Namdev, Bhagat Kabir and Sheikh Farid, but the ultimate Guru (or teacher) of a Sikh is Guru Granth Sahib which include about 10% of the verses of these Saints.
As a famous Sikh author says "Sikhism undoubtedly accepted some of the aspects of radicalized bhakti, and admitted some of its practices into its own ordained set. It did lay down spiritual love as the way to the deity, but the deity to be worshipped was neither Shiva nor Vishnu nor even any of their incarnations, nor any of the gods or goddesses of the Hindu pantheon. It was the One and the Only God, the Lord of Universes who was at once transcendent (nirguna) and immanent (saglma). Although immanent in his Creation He was yet apart from it, being its Creator. Since He in he real in the world that He had created, the world could not be considered unreal or illusionary (mithya or maya). It was real and sacred ("the abode of the True One"). It is therefore blasphemous to renounce it in quest of God. "He that is immanent in the Universe resides also within yourself. Seek, and ye shall find" (ee, 695). Renunciation of the world as a spiritual pursuit thus stood totally rejected. Celebacy was no longer countenanced, either. Full participation in life in a spirit of 'detachment' was prescribed instead. "Of all the religious rules and observances grihasthya (the homestead) is supreme. It is from here that all else is blessed" (Guru Granth Sahib, 587). Guru is paramount in bhakti as well as in Sikhism ." Excerpts taken from these books
Sikhism, its philosophy and History, edited by Daljeet Singh and Kharak Singh.
The radical Bhagats written by Daljeet Singhj ji.