From a practical viewpoint, good qualities are also necessary or the aspirant will not qualify as a disciple. If he does not qualify as a disciple, he will not be able to have a Guru, because even if he has one, he will not be able to make the most of his Guru. Certainly that if the Self decides so, even the worst of the aspirants can be transformed into the best of the disciples instantly, but more often than not, the case is that the aspirants will have to acquire good qualities to qualify as disciples.
What are those 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 regards his Guru as someone lower than the Supreme Lord Himself, he will not attain final liberation. This is difficult to understand, but I am speaking the truth. Disciples believing that their Guru is not an embodiment of the Supreme Lord are not really disciples but mere people around the physical body of that Guru. They are there like animals around a human being. Imagine pets around me while I write all these spiritual teachings on my computer and that is a good depiction of what those people look like around their Guru.
They have no idea about what their Guru is, and no idea about what their Guru is doing. They must endow their egos (their invented individualities in the form of "I am John", "I am Jane", etc.) with good qualities then. The main good quality is firm conviction that the Guru is the Supreme Lord Himself appearing in that human form. Of course, I am speaking about genuine Guru-s and not mere clowns using the appellative "Guru". Therefore, it is obvious that there must be a certain degree of understanding in the aspirant from the very start, 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 instance, 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 fruits for him at all. Not only the Mantra, but all of 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 his master.
From the first good quality called "conviction that one's own Guru is the Supreme Lord in person", the second one is derived: 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 him but with more spiritual knowledge, and things like that.
An aspirant is transformed into a real disciple when he has the aforesaid conviction then, which will generate almost automatically "obedience". Ego, specially in the West, is always very used to get his own way because one apparently knows "what is more convenient or better". A real disciple realized, from a practical viewpoint, that he has no idea what is more convenient or better in his case since he knows nothing about his own future in this heartbreaking world. He realizes that he lives at the mercy of all around him (other people, external things moving, etc.) and inside him (thoughts, anger, frustration, etc.). He has no idea what is better for him then. This realization will generate obedience at once. Disobedient disciples are never real disciples, and of course, they are not had in high esteem by any genuine Guru. They just pester their Guru like mosquitoes pester 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 target, and no spiritual enlightenment happens to them because the Deity called "their own Self" is simply "not pleased" with them.
From those two good qualities I mentioned, other good qualities will be developed as well. All these good qualities make an aspirant qualify 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 to cheat in this context, that is, either one is a real disciple or one is not.
If one is not a real disciple, the process of final liberation will not proceed rightly and one will remain in bondage. In this case, what is the point of having a Guru then? One will get his own way all the time like the rest of ordinary people on this planet, but he will never be Free in the truest sense of word.
Guru Gabriel Pradīpaka in The Paramārthasāra of Abhinavagupta