All persons do not see or realize the Brahman in their life-time. Certain qualifications are absolutely necessary.
(1) Mumuksha or intense desire to get free. He, who thinks that he is bound and that he should get free from bondage and works earnestly and resolutely to that end;and who does not care for any other things, is qualified for the spiritual life.
(2) Virakti or a feeling of disgust with the things of this world and the next. Unless a man feels disgusted with the things, emoluments and honors, which his action would bring in this world and the next, he has no right to enter into the spiritual realm.
(3) Antarmukhata (introversion). Our senses have been created by God with a tendency to move outward and so, man always looks outside himself and not inside. He who wants self-realization and immortal life, must turn his gaze inwards, and look to his inner Self.
(4) Catharsis from (Purging away of) sins. Unless a man has turned away from wickedness, and stopped from doing wrong, and has entirely composed himself and unless his mind is at rest, he cannot gain self-realization, even by means of knowledge.
(5) Right Conduct. Unless, a man leads a life of truth, penance and insight, a life of celibacy, he cannot get God-realization.
(6) Preferring Shreyas, (the Good) to Preyas (the Pleasant). There are two sorts of things viz., the Good and the Pleasant; the former deals with spiritual affairs, and the latter with mundane matters. Both these approach man for acceptance. He has to think and choose one of them. The wise man prefers the Good to the Pleasant; but the unwise, through greed and attachment, chooses the Pleasant.
(7) Control of the mind and the senses. The body is the chariot and the Self is its master; intellect is the charioteer and the mind is the reins; the senses are the horses and sense-objects their paths. He who has no understanding and whose mind is unrestrained, his senses unmanageable like the vicious horses of a charioteer, does not reach his destination (get realization), but goes through the round of births and deaths; but he who has understanding and whose mind is restrained, his senses being under control, like the good horse of a charioteer, reaches that place, i.e., the state of self-realization, when he is not born again. The man, who has understanding as his charioteer (guide) and is able to rein his mind, reaches the end of the journey, which is the supreme abode of the all-pervading, Vishnu (lord).
(8) Purification of the mind. Unless a man discharges satisfactorily and disinterestedly the duties of his station in life, his mind will not be purified and, unless his mind is purified, he cannot get self-realization. It is only in the purified mind that Viveka (discrimination between the Unreal and the Real), and Vairagya (Non-attachment to the unreal) crop up and lead on the self-realization. Unless egoism is dropped, avarice got rid of, and the mind made desireless (pure), self-realization is not possible. The idea that 'I am the body' is a great delusion, and attachment to this idea is the cause of bondage. Leave off this idea and attachment therefore, if you want to get to the Self-realization.
(9) The necessity of a Guru. The knowledge of the self is so subtle and mystic, that no one could, by his own individual effort ever hope to attain it. So the help of another person-Teacher, who has himself got self-realization is absolutely necessary. What others cannot give with great labour and pains, can be easily gained with the help of such a Teacher; for he has walked on the path himself and can easily take the disciple, step by step on the ladder of spiritual progress.
(10) And lastly, the Lord's Grace is the most essential thing. When the Lord is pleased with any body, He gives him Viveka and Vairagya; and takes him safe beyond the ocean of mundane existence, "The Self cannot be gained by the study of Vedas, nor by intellect, nor by much learning. He, whom the Self chooses, by him, it is gained. To him the Self reveals Its nature", says the Katha Upanishad.
Source: Shri Sai Sarcharitra