The guru who leads you to liberation and enlightenment is someone about whom you feel: "With this one I can practice guru devotion." You then make the decision to establish a guru-disciple relationship and take teachings from them. A guru-disciple relationship does not depend on whether or not you personally go to ask the person to become your guru. For example, there are thousands of people who take teachings from His Holiness the Dalai Lama. Each one of them doesn't go to His Holiness and ask: "Will you be my guru?" According to tradition, the very first time you take teachings from a guru, you may ask their permission to attend a teaching, in case there are some grounds for refusal, but only if there is time. It is mainly up to you.
Before taking teachings on guru devotion, you may find the idea of the guru-disciple relationship uncomfortable and difficult to relate to. After accepting the relationship and hearing teachings, your view may be different. If you practice guru devotion from your side, you will no longer hold your previous view; your way of thinking will completely change. A lot depends on the disciple's way of thinking and understanding of the teachings.
As explained by His Holiness the Dalai Lama, and by Lama Tsongkhapa in the guru devotion section of Lamrim Chenmo, there are two ways to see the guru as Buddha. If you understand and practice these two methods well, you are able to see the nature of the guru as Buddha. The first way is to train your mind to see the qualities of the guru; the second is to see the guru's mistakes, but use them to develop devotion. These two ways of establishing the realization of the guru as Buddha are explained very clearly and perfectly in Lama Tsongkhapa's Lamrim Chenmo.
Why do you need to see the guru as Buddha? Because you, the disciple, want profit and do not want loss. This "profit" includes all the happiness of this life, which is the aim of an ordinary being; the happiness of future lives, the aim of the being of small scope; liberation from samsara, the aim of the being of medium scope; and great liberation, or enlightenment, for all sentient beings, the aim of the being of great scope. "Loss" refers to all the failures you experience when you do not practice these means to achieve happiness. All these levels of happiness and all the means of achieving them are contained in the statement: You, the disciple, want profit and do not want loss.
The teachings explain that even if the guru is born in hell, if the disciple continuously practices guru devotion, the disciple receives blessings to develop their mind and have attainments on the path: the disciple profits. The essential means to achieve enlightenment in one very brief lifetime is to see the guru as the essence of all buddhas. However, in order to develop the devotion to see the guru as Buddha, you have to stop all your wrong conceptions of the guru and see only their qualities. This is extremely important.
Lama Tsongkhapa explains that allowing one wrong thought to arise toward the guru, even for one second, destroys your perfections; in other words, it causes any realizations you already have to degenerate and interferes with the generation of new realizations of the path and the result of enlightenment. Even though the guru has many qualities, looking from the side of his mistakes obscures all those qualities. Seeing some small mistake obscures all the rest of the qualities, so that you see only mistakes. This is training your mind in a negative way. On the other hand, looking at the qualities of the guru and generating devotion cause you to achieve all the realizations of the graduated path up to enlightenment.
Relate this to yourself: You have oceans of mistakes, but few good qualities. Looking at yourself only in terms of your few qualities obscures all your mistakes so that you see only your good qualities. This is how your mind has been trained to see yourself. So if you look at the guru in the same way, your mind can be trained to develop guru devotion.
Why is the practice of guru devotion so important? Someone may try to do a lamrim or shamatha retreat and fail after some time because many disturbances arise. Or someone may be living in ordination, with great ambitions to benefit sentient beings and the teachings just like Lama Tsongkhapa, Lama Atisha or Guru Shakyamuni Buddha; however, even though the wish is there, it does not happen because there are so many obstacles. Such experiences are due to having made mistakes in the practice of guru devotion in past lives or in this life. Even though you may have all the necessary conditions to practice Dharma, many obstacles arise and you fail. Because in past lives you did not practice guru devotion correctly, these shortcomings are experienced in this life and for many lifetimes, on and on and on. Even though you meet Dharma in the future, you still experience obstacles. Everything, from the happiness of this life up to enlightenment, depends on the root of guru devotion. Guru devotion is essential for the completion of listening, reflecting and meditation practice.
Because of incorrect practice of guru devotion in the past, you create the result similar to the cause, which means repeating the same mistake for many lives, again and again. Even on those rare opportunities when you meet a guru and the teachings, again you commit the same mistake in your practice. Therefore, it is very important, even though you may have made many mistakes, to make a determination not to make them again. Making the strong determination to practice guru devotion correctly now and in the future is the remedy that stops these mistakes happening again. The practice of guru devotion is emphasized so much in both sutra and tantra teachings because wrong conceptions of the guru are the greatest obstacles to happiness.
How can we understand that it is possible to achieve liberation? When you understand emptiness, when you recognize the objects held by simultaneously born ignorance as false and empty, you can understand how it is possible to achieve liberation. You then develop one hundred percent faith that ignorance, and the wrong conceptions arising from that ignorance, can be eliminated. You develop firm faith that liberation is possible. Through understanding the two stages of the graduated path of Highest Yoga Tantra, especially the second stage, you understand more clearly the result of the four kayas and develop even more faith that liberation is possible. You then feel much more faith when you recite such prayers as Calling the Guru from Afar.
It is very practical to think as Kachen Yeshe Gyaltsen advised: "I am so fortunate to be able to find even a few qualities in the guru. If even my impure mind is able to see this many qualities, how many qualities must be seen by someone whose mind is purer." Think of how many nonvirtuous thoughts arise in each day. Your mind is constantly overwhelmed by negative karma and disturbing thoughts, which obscure your mind and create obstacles. Think, “With a mind so heavily obscured by impure karma, it is a miracle that I am able to see even this much purity in the guru. I am very fortunate.”
Generally, even the appearance of purity or beauty in sense objects depends on your karma, on your mind. Since the appearance of everything depends on your mind, on your karma, there is no way for Buddha to manifest other than according to your karma; there is no other way for you to see Buddha. Now, since your karma is impure (you can see this by thinking about even one day of your life), the only way Buddha can manifest is in an ordinary form, which means having mistakes and delusions.
This is extremely kind. If Buddha manifested in a lower form, you could not recognize him or receive teachings from him; if Buddha manifested in a higher form, you would not have the karma to see him. According to your karma, these gurus in ordinary aspects, with mistakes and delusions, are the only ones who can reveal the teachings to you. These gurus lead you to enlightenment when you put their teachings into practice. They are the only ones who lead you to enlightenment by directly teaching you; there is no other aspect from which you can receive teachings. Without them, there is no way to receive teachings and put them into practice; no way to achieve liberation from samsara; no way to achieve enlightenment. Think how kind the guru is!