Guru Granth Sahib the sacred book of the Sikhs contains four poems of Trilochan, 62 of Namadeva and 240 Sakhis and 227 padas of Kabir. Most of the characteristic teachings of Sikhism like monotheism, crusade against idolatry and caste, externalism (bhaiachara), ritualism could be easily traced to these saint poets, specially Kabir. Kabir appears to be a contemporary of Guru Nanak.
Guru Granth Sahib for the Sikhs is what the Bible is to the Christians, the Quoran to the Muslims, the Veda to the Brahmins. It is the most sacred scripture for the Sikhs and they even pray the Guru Granth Sahib.
It contains Bani which stands on the level of `the Word` of the Christian and of the followers of Shabda Brahma and of the Saivites. Guru Nank himself had composed a number of songs, the best of them may be named Japji, Asa-di-var, Rahi-rasa Patti, Dakani Omkara, Siddha Gosthi and Bara Mah.
Other Gurus after Guru Nanak have also added their compositions. Guru Granth Sahib was composed in 1604 by Guru Arjan Dev who was assisted by the great devotee Bhai Gurdas. It was written in Gurmukhi Script so that the Sikhs may remain Guru-centred. Guru Granth Sahib includes not only the compositions of Gurus but also of many Saint poets. It includes verses of Ramanand, Jaideva, Namadeva, Trilochan, Veni, Dhanna, Pipa, Sain, Kabir, Rai Das, Shaikh Bhikhaji, Sadhna, Surdas, Poona Nane and of Muslim Sufis.
However, the compositions of Kabir are far more numerous than of any other non-Sikh composers. 243-245 Sakhis and 227 padas of Kabir have been included in Guru Granth Sahib." This shows the great esteem in which Kabir was held by Sikh Gurus. Kabir was a non-Vedic Hindu influenced by Gorakhnath and some Buddhist poets.
Hence, much of Sikhism has to be understood and interpreted in terms of Saints` religious philosophy. However, Sikhism in course of its historical development has to be understood as an independent religion like Jainism and Buddhism. But it is an Indian religion and wholly embedded in the culture and tradition of India, more non-Vedic than Vedic.