Four Varnyas (Four Castes)

Every man has in himself all the four Dharmas, but one predominates, in one he is born and that strikes the note of his character and determines the type and cast of all his actions; the rest subordinated to the dominant type and helps to give it its complement.

First of all, one should possess characteristics of Brahmana – a man of knowledge.

Brahmatejas: Jnanalipsa, Jnanaprakaso, Brahmavarcasyam, Sthairyam.
Jnanalipsa. I give only the dominant qualities of the type in these definitions: The Purna Yogin does not reduce his nature to inaction but perfects it and uplifts in order to place it at the service of the Ishwara in His Lila. He accepts the Jnanalipsa and purifying it of desire turns it into a divine reaching out towards Prakasha of knowledge; this divine desireless reaching out of Brahman in personality to Brahman in the visaya or object, is the new sense which lipsa acquires in the language of the siddha.
Jnanaprakaso. Jnana includes both the Para and the Apara Vidya; the knowledge of the Brahman in Himself and the knowledge of the world; but the Yogin, reversing the order of the worldly mind, seeks to know Brahman first and, through Brahman, the world. Scientific knowledge, worldly information and instruction are to him secondary objects, not as it is with the ordinary scholar and scientist, his primary aim. Nevertheless these too we must take into our scope and give room to God's full joy in the world. The methods of the Yogin are also different for he tends more and more to the use of direct vision and the faculties of the Vijnana and less and less to intellectual means. The ordinary man studies object from outside and infers its inner nature from the results, his external study. The Yogin seeks to get inside the object, know it from within and use external study only as a means of confirming his view of the outward action resulting from an already known inner nature.
Brahmavarcasyam. Brahmavarcasya is the force of Jnana working from within man, which tends to manifest the divine light, the divine power, the divine qualities in the human being.
Sthairyam. Sthairyam is the capacity of fixity in Jnana; the man who is sthira is able to hold the light and power that enters into him without stumbling or being dazzled and blinded by their shock and to receive and express the divine forces in himself without being carried away by them and subjected to the blind rushing stream of Prakriti. He has the dharanasamarthyam and does not from incapacity of the Adhara lose or spill these things as they enter into him.

Kshatratejas: Abhayam, Sahasam, Yasolipsa, Atmaslagha.
Abhayam is the passive freedom from fear which with a bold calmness meets and receives every menace of danger and shock of misfortune.
Sahasam is the active courage and daring which shrinks from no enterprise however difficult or perilous, and cannot be dismayed or depressed either by the strength or the success of the opposing forces.
By Yasas is meant victory, success and power. Although the Kshatriya must be ready to face and accept defeat, disaster and suffering, yet his objective, the thing towards which he moves, is yasas. He enters the field to conquer, not to suffer. Suffering is only a means towards victory. Here again the reaching out, the lipsa must come to be free from desire and consist in the divine reaching out of God within to His self-fulfilment as the Kshatriya. Therefore the Kshatriya must manifest in himself the nature of the Brahmin, Jnana and sthairyam, since without knowledge in some form, desire cannot perish out of the system.
AtmaSliighii in the unpurified Kshatriya is pride, self-confidence, and the knowledge of his own might. Without these qualities the Kshatriya becomes deficient in force and fails to effect himself in type and action but with purification it becomes no longer the slagha of the aham, but the slagha of the Atman, the divine self within rejoicing in the Shakti of God and its greatness and its power as it pours itself out in battle and action through the human adhara.

Vaishyashakti: Diinam, Vyayab, Kausalam, Bhogalipsii.
Danam and pratidanam are the especial Dharma of the Vaishya; his nature is the nature of the lover who gives and seeks; he pours himself out on the world in order to get back what he has given increased a hundredfold. Vyaya is his capacity to spend freely for this purpose without any mean and self-defeating miserliness in the giving. Kausalam is the dexterity and skill which is able so to arrange the means, the equipment, the action as to produce the greatest results possible and the best arranged results. Law, arrangement, suiting of means to ends, of expenditure to return, are the joy of the Vaishya. Bhoga is his object; possession and enjoyment, not merely of physical things, but all enjoyment, enjoyment of knowledge, of power, of self-giving, of service, comes within its scope. The Vaishya, purified and liberated, becomes the supreme giver and lover and enjoyer, Krishna's amsa preserving and making the most of the world. He is the Vishnushakti, as the Brahmana is the Shivashakti and the Kshatriya is the Rudrashakti.

Shudrashakti: Kamah, Prema, Dasyalipsa, Atmasamarpanam.
The Shudra is God descending entirely into the lower world and its nature, giving himself up entirely for the working out of God's Lila in Matter and in the material world. From this standpoint he is the greatest of the four Shaktis, because his nature goes direct towards complete Atmasamarpana; but the Shudra bound, has cut himself off from knowledge, power and skill and lost himself in the tamoguna. He has to recover the Brahmana, Kshatriya and Vaishya in himself and give them up to the service of God, of man, of all bengs. The principle of Kamah or desire in him must change from the seeking after physical well-being and self-indulgence to the joy of God manifest in Matter. The principle of Prema must find itself and fulfil itself in Dasyalipsa and Dtmasamarpana in the surrender of himself to God and to God in manand the selfless service of God and of God in man. The Shudra is the master spirit of the Kali, as is the Vaishya of the Dwapara, the Kshatriya of the Treta and the Brahmana of the Satya.

The nature of Brahmana is knowledge, Kshatriya – strength and courage, Vaishya – ability and capacity to work, Shudra – surrender and service. A perfect being possesses all of them since they all are necessary for doing perfect work.

Chapter Shakti. Section Four Varnyas.
Sri Aurobindo