This question usually comes from a person who is in the knowledge path – Jnana Yogi. There are many paths to reach God. And Guru is the guiding light. There are many types of people too. Everyone has his or her own style and approach towards any situation. Actually speaking, no true guru or God needs anything from you, let alone worship.
Now, a person of emotional nature, who chants praises of God – usually the form that his mind gets connected to easily, melts himself or herself into that being or object of worship. These people need an object to worship. Human mind needs forms to associate with. This is fundamental. It recognizes forms and connects to forms. Human constitution uses all faculties such as body, mind and intellect to connect to the chosen form. And when the connection through faith increases, individual personality takes a back seat. The individual starts to merge with the object of worship. Non-duality happens. When oneness takes root, often the need for any of the individual faculties that the individual used for the primary connection also becomes redundant. Everything dissolves into oneness. This is the advantage of bhakti Yoga. Usually, Bhakti Yogis merge with supreme consciousness much faster than the other paths such as knowledge, sadhana (spiritual practices) and service. The tranquility and strength that they achieve through surrender cannot be fathomed by the practitioners of other types of paths.
Likewise, the elevation that knowledge gives – based on duality is not understandable to a Bhakthi Yogi too. Experiencing God using the path of knowledge is like the pole of the pole vault. The pole is only used to lift one beyond the bar. Then, the pole of knowledge is shed when the bar is crossed. Then it is just a fall into the lap of Infinity or God. But, if the Yogi holds on to the pole and refuses to let go, handicap happens in the game. He stays with his pole and cannot win God.
There is a saying “If God and Guru come together, whom to greet first?” The answer automatically happens “Guru, because he is the one who brought and guided me to God”.
So, worshipping the Guru, considering him as representing the Lord Almighty, or personification of the Lord is definitely the path of those who are inclined to Bhakti or devotional path of spirituality. Understand that all paths are suitable for someone. All paths are not suitable for everyone. So, do not judge from your level. If you do, you will only get more disillusioned. You may not understand the pleasure that a bhakti yogi derives from any acts of devotional nature. They often do not have duality. They become one with the object of their worship faster than other paths.
The knowledge path keeps duality longer than other paths because, intellect is the faculty used to digest knowledge and intellect is associated to our limited system. This constitution of ours which is tangible and that we call with a name is associated with a form. Intellect alienates and analyses. Intellect creates walls. When knowledge becomes wisdom, that means each unit of knowledge intake is digested well, and it merges into our constitution, duality slowly starts to dissolve. Oneness takes root.
Understand one thing clearly. No true gurus or god needs anything from people including worshipping their perishable physical form. But, for disciples, it is reconfirmation, confidence and it helps in maintaining their faith. This is why they do it. Every practice has its value only if it is done from the heart. If mechanically, ritualistically done, no activity will have any value.