Bhakti is the substance of Spiritualism

It is said in the Vedas that the power of all the Hindu deities are inherent in the form of the Sadguru. So there is nothing wrong if only the Sadguru is worshiped at home or if He is worshiped in the form and manner of any deity. Sikh devotees sacrificed their lives happily for their Gurus because it was their belief that the Guru is eternal and will always be with them. It is absolutely necessary to have immense faith in the Sadguru and worship Him as God. At the same time it is required to simplify the method of worship of the Sadguru.

Whereas Puja is a methodology, Bhakti is the substance of spiritualism.

Source: BABA MAY I ANSWER by Guruji Dr.C.B Satpathy