According to the text, why is having a Guru in a physical form so important for a devotee?

Chapter 11 of the Sai Satcharitra explains that a physical Guru is necessary for a devotee who also possesses a physical body. The text presents this as a determination of the scriptures, stating, "for the formless, the formless is suitable." As detailed in chunk 2, it argues that devotion cannot truly manifest without meditation on a Saguna, or manifest, form. Until loving devotion occurs through this process, the "bud of the mind does not open," meaning spiritual growth and realization remain inaccessible to the worshipper.