One of the brothers, Jagāi, was astonished to see this behavior of Nityānanda Prabhu, and he at once fell down at His feet and asked Him to pardon his sinful brother. When Mādhāi again attempted to hurt Nityānanda Prabhu, Jagāi stopped him and implored him to fall down at His feet. In the meantime the news of Nityānanda's injury reached the Lord, who at once hurried to the spot in a fiery and angry mood. The Lord immediately invoked His Sudarśana cakra (the Lord's ultimate weapon, shaped like a wheel) to kill the sinners, but Nityānanda Prabhu reminded Him of His mission. The mission of the Lord was to deliver the hopelessly fallen souls of Kali-yuga, and the brothers Jagāi and Mādhāi were typical examples of these fallen souls. Ninety percent of the population of this age resembles these brothers, despite high birth and mundane respectability. According to the verdict of the revealed scriptures, the total population of the world in this age will be of the lowest śūdra quality, or even lower. It should be noted that Śrī Caitanya Mahāprabhu never acknowledged the stereotyped caste system by birthright; rather, He strictly followed the verdict of the śāstras in the matter of one's svarūpa, or real identity.
When the Lord was invoking His Sudarśana cakra and Śrīla Nityānanda Prabhu was imploring Him to forgive the two brothers, both the brothers fell down at the lotus feet of the Lord and begged His pardon for their gross behavior. The Lord was also asked by Nityānanda Prabhu to accept these repenting souls, and the Lord agreed to accept them on one condition, that they henceforward completely give up all their sinful activities and habits of debauchery, both the brothers agreed and promised to give up all their sinful habits, and the kind Lord accepted them and did not again refer to their past misdeeds.
This is the specific kindness of Lord Caitanya. In this age no one can say that he is free from sin. It is impossible for anyone to say this. But Lord Caitanya accepts all kinds of sinful persons on the one condition that they promise not to indulge in sinful habits after being spiritually initiated by the bona fide spiritual master.
(Srimad Bhagavatam--introduction).

The almighty Personality of Godhead, Śrī Kṛṣṇa, having observed that a great danger was befalling His unalloyed devotees, who were fully surrendered souls, at once took up His Sudarśana disc to protect them.
The brahmāstra, the supreme weapon released by Aśvatthāmā, was something similar to the nuclear weapon but with more radiation and heat. This brahmāstra is the product of a more subtle science, being the product of a finer sound, a mantra recorded in the Vedas. Another advantage of this weapon is that it is not blind like the nuclear weapon because it can be directed only to the target and nothing else. Aśvatthāmā released the weapon just to finish all the male members of Pāṇḍu's family; therefore in one sense it was more dangerous than the atomic bombs because it could penetrate even the most protected place and would never miss the target. Knowing all this, Lord Śrī Kṛṣṇa at once took up His personal weapon to protect His devotees, who did not know anyone other than Kṛṣṇa. In the Bhagavad-gītā the Lord has clearly promised that His devotees are never to be vanquished. And He behaves according to the quality or degree of the devotional service rendered by the devotees. Here the word ananya-viṣayātmanām is significant. The Pāṇḍavas were cent percent dependent on the protection of the Lord, although they were all great warriors themselves. But the Lord neglects even the greatest warriors and also vanquishes them in no time. When the Lord saw that there was no time for the Pāṇḍavas to counteract the brahmāstra of Aśvatthāmā, He took up His weapon even at the risk of breaking His own vow. Although the Battle of Kurukṣetra was almost finished, still, according to His vow, He should not have taken up His own weapon. But the emergency was more important than the vow. He is better known as the bhakta-vatsala, or the lover of His devotee, and thus He preferred to continue as bhakta-vatsala than to be a worldly moralist who never breaks his solemn vow.
(Srimad Bhagavatam----1:8:13----translation and purport).

Sudarśana: This wheel which is accepted by the Personality of Godhead (Viṣṇu or Kṛṣṇa) as His personal weapon is the most powerful weapon, greater than the brahmāstras or similar other disastrous weapons. In some of the Vedic literatures it is said that Agnideva, the fire-god, presented this weapon to Lord Śrī Kṛṣṇa, but factually this weapon is eternally carried by the Lord. Agnideva presented this weapon to Kṛṣṇa in the same way that Rukmiṇī was given by Mahārāja Rukma to the Lord. The Lord accepts such presentations from His devotees, even though such presentations are eternally His property. There is an elaborate description of this weapon in the Ādi-parva of the Mahābhārata. Lord Śrī Kṛṣṇa used this weapon to kill Śiśupāla, a rival of the Lord. He also killed Śālva by this weapon, and sometimes He wanted His friend Arjuna to use it to kill his enemies (Mahābhārata, Virāṭa-parva 56.3).
(Srimad Bhagavatam----1:9:6-7---- purport).

Śrī Caitanya Mahāprabhu has described the vaiṣṇava-aparādha, or offense to a Vaiṣṇava, as "the mad elephant offense." One should be very careful not to offend a Vaiṣṇava or a brāhmaṇa. Even the great yogī Durvāsā was harassed by the Sudarśana cakra when he offended the Vaiṣṇava Mahārāja Ambarīṣa, who was neither a brāhmaṇa nor a sannyāsī but an ordinary householder. Mahārāja Ambarīṣa was a Vaiṣṇava, and consequently Durvāsā Muni was chastised.
(Srimad Bhagavatam----4:26:24---- purport).

After hearing from the sun and moon demigods about Rāhu's attack, the Supreme Personality of Godhead, Viṣṇu, engages His disc, known as the Sudarśana cakra, to protect them. The Sudarśana cakra is the Lord's most beloved devotee and is favored by the Lord. The intense heat of its effulgence, meant for killing non-Vaiṣṇavas, is unbearable to Rāhu, and he therefore flees in fear of it. During the time Rāhu disturbs the sun or moon, there occurs what people commonly know as an eclipse.
The Supreme Personality of Godhead, Viṣṇu, is always the protector of His devotees, who are also known as demigods. The controlling demigods are most obedient to Lord Viṣṇu, although they also want material sense enjoyment, and that is why they are called demigods, or almost godly. Although Rāhu attempts to attack both the sun and the moon, they are protected by Lord Viṣṇu. Being very afraid of Lord Viṣṇu's cakra, Rāhu cannot stay in front of the sun or moon for more than a muhūrta (forty-eight minutes). The phenomenon that occurs when Rāhu blocks the light of the sun or moon is called an eclipse. The attempt of the scientists of this earth to go to the moon is as demoniac as Rāhu's attack. Of course. their attempts will be failures because no one can enter the moon or sun so easily. Like the attack of Rāhu, such attempts will certainly be failures.
(Srimad Bhagavatam----5:24:3---- translation and purport).

There are innumerable universes in the material world, and there are innumerable Lord Brahmās, Lord Śivas and other demigods. All of them rotate within this material world under the supreme direction of the Personality of Godhead. Therefore no one is able to compete with the strength of the Lord. Lord Śiva also refused to protect Durvāsā, for Lord Śiva also was under the rays of the Sudarśana cakra sent by the Supreme Personality of Godhead.
(Srimad Bhagavatam----9:4:56---- purport).

In this chapter we find Mahārāja Ambarīṣa offering prayers to the Sudarśana cakra and we find how the Sudarśana cakra became merciful to Durvāsā Muni.
By the order of the Supreme Personality of Godhead, Viṣṇu, Durvāsā Muni immediately went to Mahārāja Ambarīṣa and fell at his lotus feet. Mahārāja Ambarīṣa, being naturally very humble and meek, felt shy and ashamed because Durvāsā Muni had fallen at his feet, and thus he began to offer prayers to the Sudarśana cakra just to save Durvāsā. What is this Sudarśanacakra? The Sudarśana cakra is the glance of the Supreme Personality of Godhead by which He creates the entire material world. Sa aikṣata, sa asṛjata. This is the Vedic version. TheSudarśana cakra, which is the origin of creation and is most dear to the Lord, has thousands of spokes. This Sudarśana cakra is the killer of the prowess of all other weapons, the killer of darkness, and the manifester of the prowess of devotional service; it is the means of establishing religious principles, and it is the killer of all irreligious activities. Without his mercy, the universe cannot be maintained, and therefore the Sudarśana cakra is employed by the Supreme Personality of Godhead. When Mahārāja Ambarīṣa thus prayed that the Sudarśana cakrabe merciful, the Sudarśana cakra, being appeased, refrained from killing Durvāsā Muni, who thus achieved the Sudarśana cakra's mercy. Durvāsā Muni thus learned to give up the nasty idea of considering a Vaiṣṇava an ordinary person (vaiṣṇave jāti-buddhi).
(Srimad Bhagavatam---9:5: summary).

O Sudarśana wheel, you are religion, you are truth, you are encouraging statements, you are sacrifice, and you are the enjoyer of the fruits of sacrifice. You are the maintainer of the entire universe, and you are the supreme transcendental prowess in the hands of the Supreme Personality of Godhead. You are the original vision of the Lord, and therefore you are known as Sudarśana. Everything has been created by your activities, and therefore you are all-pervading.
The word sudarśana means "auspicious vision." From Vedic instructions we understand that this material world is created by the glance of the Supreme Personality of Godhead (sa aikṣata, sa asṛjata). The Supreme Personality of Godhead glanced over the mahat-tattva, or the total material energy, and when it was agitated, everything came into existence. Western philosophers sometimes think that the original cause of creation was a chunk that exploded. If one thinks of this chunk as the total material energy, the mahat-tattva, one can understand that the chunk was agitated by the glance of the Lord, and thus the Lord's glance is the original cause of material creation.
(Srimad Bhagavatam----9:5:5----translation and purport).