From a practical point of view, good qualities are also necessary or the aspirant will not qualify as a disciple. If he does not qualify as a disciple, he cannot have a Guru, because even if he has one, he cannot take full advantage of his Guru. Certainly, if the Self so decides, even the worst aspirant can be transformed into the best disciple instantly, but most of the time it is the case that aspirants will have to acquire good qualities to qualify as disciples.
What are these good qualities? First of all: The disciple must be convinced that his Guru is the Supreme Lord appearing as a person endowed with a physical body, etc. If he considers his Guru to be lower than the Supreme Lord Himself, he will not attain final liberation. This is difficult to understand, but I am speaking the truth. Disciples who think that their Guru is not a personification of the Supreme Lord are not really disciples but merely people around the physical body of that Guru. They are there like animals around a human being. Imagine pets around me as I type all these spiritual teachings on my computer and that is a good representation of how such people look around their Guru.
They have no idea what their Guru is, and no idea what their Guru is doing. They must endow their egos (their made-up individualities in the form of "I am John," "I am Jane," etc.) with good qualities then. The main good quality is the firm conviction that the Guru is the Supreme Lord Himself appearing in that human form. Of course, I am talking about genuine Guru-s and not about mere clowns using the appellation "Guru." Therefore, it is obvious that there must be a certain degree of understanding in the aspirant from the very beginning, or he will not qualify as a disciple. To be a disciple, first of all, he must be convinced that his Guru is the Supreme Lord teaching him.
For example, if he received a Mantra from that Guru, he is convinced that he received the Mantra from the Supreme Lord Himself. If the aspirant does not have that attitude, he is not a disciple, and as a result, the Mantra will not bear any fruit at all. Not only the Mantra, but all his practices will not bear any fruit if he lacks that conviction in the divinity of his Guru. He will remain with such a Guru like a pet with its master, or even worse because at least a pet generally obeys its master.
From the first good quality called "conviction that one's Guru is the Supreme Lord Himself" comes the second good quality, obedience. No obedience is possible if the aspirant thinks that his Guru is an ordinary person or even if he thinks that his Guru is a mere mortal like himself but with more spiritual knowledge, and so on.
An aspirant becomes a real disciple when he has the above conviction then, which will almost automatically generate "obedience." The ego, especially in the West, is always very used to getting its way because one apparently knows "what is most convenient or best." A real disciple realized, from a practical point of view, that he has no idea what is most convenient or best for him, since he knows nothing about his own future in this bleak world. He realizes that he lives at the mercy of everything around him (other people, external moving things, etc.) and within him (thoughts, anger, frustration, etc.). He has no idea what is best for him then. This realization will generate obedience right away. Disobedient disciples are never real disciples, and of course, they are not held in high esteem by any genuine Guru. They only bother their Guru like mosquitoes bother a person living in a jungle. They always have a better opinion, a better idea than their own Guru, and consequently, they always miss the mark, and no spiritual enlightenment comes to them because the Deity called "their own Self" is simply "not pleased" with them.
From these two good qualities that I mentioned, other good qualities will also develop. All these good qualities qualify an aspirant as a disciple.
If he is not a real disciple, he will not be able to receive the instruction of his Guru properly, and no final liberation will occur. There is no way of cheating in this context, that is, one is either a real disciple or one is not.
If one is not a real disciple, the process of final liberation will not proceed properly and one will remain in bondage. In this case, what is the point of having a Guru then? One will have his way all the time like the rest of the ordinary people on this planet, but one will never be Free in the truest sense of the word.
Guru Gabriel Pradīpaka in The Paramārthasāra of Abhinavagupta